Big thanks to James "OPT" Fitzgerald and his website, Optimum Performance Training. I hope to add/adjust to this as time goes on, as much of this is specifically designed for his amazing training techniques and program. OPT is the man, and any adjustments I eventually make will probably be in the name of toning the info down to MY level. ;)

How to read the workout.
What does A1, A2, B1, B2, mean?  How do I follow the sets?  What does the rest portion mean?
We will use a typical multi-facet resistance training workout that would be prescribed on this Blog:
A1. High Bar Back Squat @ 30X0, 4-6 reps x 5 sets, rest 120 sec
A2. Chest to Bar Chin-ups, AMRAP x 5 sets, rest 120 sec
B1. KBS – 2 pd, 21 reps x 4 sets, rest 30 sec
B2. Ring Dips, 21 reps x 4 sets, rest 30 sec
In this workout you move through exercise A1 at the rx’d tempo, for the rx’d reps, you then rest for the rx’d amount of time (exactly) after the set is completed. Following the rest you do exercise A2 at the rx’d tempo, for the rx’d reps, you then rest for the rx’d amount of time after the set is completed. You then proceed back to A1. This alternation continues until the rx’d number of sets are completed for each exercise. For the above, this would mean 5 sets through A1/A2, with 120 seconds rest between each set.
Once you have completed the A1/A2 series, you move to B1. You start B1, 120 seconds after your last set of A2. This style of workout can go into C1/C2, D1/D2, or A1/A2/A3/A4/A5/A6. Nothing changes, you simply following the rx’d order of exercises, the rx’d tempo, the rx’d reps, the rx’d sets.

What the hell does 50X0 mean?
It signifies a certain tempo. There are many examples like this – 21X0/1010/5010/etc. You simply have to take the exercise and correlate the timing (i.e. the numbers – 30X0) to it.
For example, if a bench press or back squat is rx’d at 30X0, it means that from the top of the movement, you should take 3 seconds (1 one thousand, 2 one thousand, etc.) to reach the end point of the exercise (bar to chest in the bench press or full depth for the squat). So, the first number signifies the lowering portion of ANY exercise. 
The second number signifies if there is any PAUSE in the bottom position. Because this example says 0, it means that it is simply 3 seconds down, 0 pause, and then back up. If the tempo was 31X0, then you would have to pause for 1 second at the bottom of the movement. If it was 32X0, then you would have to pause for 2 seconds, and so on.
The third number signifies the time in which to raise the load. When it says “X” as the third number, it means to accelerate the load as fast as possible – regardless of how fast the weight is actually moving; intention to accelerate is most important. If the number is 2020, as sometimes rx’d for GHD sit-ups or back extensions, then you have to take 2 seconds to lower fully, 0 pause in the full stretch position, then take 2 seconds to come back to the top (you are capable of going faster, but that is not what is being asked, so follow the numbers), with 0 sec rest before going into the next rep.
There is also a case when you could be asked to do a 3010 tempo - on the bench press for example (because it is simple). When it says 3010, the third number is critical, because it means that for whatever the rep range is, you MUST take the rx’d time to raise the load, which would be 1 second in this example. This type of tempo does not allow for maximal efforts within sets, as you HAVE TO MAINTAIN a certain cadence for the reps.
The last number, as you may have guessed, signifies any pause at the top of the movement. If it says 30X1 for a weighted chin-up (or pull-up, same thing), then you have to hold your chin over the bar for one second before lowering for 3 seconds to full arm extension.
Also, you have to LEARN to read the number, then apply it to the given exercise. Chin-ups, for example, are a special case - there are other examples as well (i.e. deadlift). Chin-ups begin with the raising portion first, not like a back squat or bench press. So, if the tempo is 30X0, the first thing you look for is NOT the 3 second prescription, but the X, meaning that you begin with the third number for this exercise, not the first one.
Why do we Rx tempos?
We do it dependent on what the Coach wants the training response to be from the workout. It is done to control intensity, overload certain areas of a movement/body part, improve technique on movements, ease the load on the joints, variability, transfer to other parts of CrossFit (i.e. back squat - 1,1,1,1,1 is MUCH different than high bar back squat @ 40X1 - 2-3 reps x 5 sets...and side note, endurance on the squat at that tempo is one thing that WILL take the CF'er to another level as it carries over to so many things).

Repetitions - What weight do I start at for each exercise of the workout?
A1. High Bar Back Squat @ 30X0, 4-6 reps x 5 sets, rest 120 sec
A2. Chest to Bar Chin-ups, AMRAP x 5 sets, rest 120 sec
B1. KBS – 2 pd, 21 reps x 4 sets, rest 30 sec
B2. Ring Dips, 21 reps x 4 sets, rest 30 sec
Well, for this example, there is only one exercise you need to choose a weight for – the back squat. So, we will use the example of someone who can back squat 300 lbs for 1 rep (1RM). The loading percentages will depend on many things for a given exercise – training age, training status, gender, muscle group, exercise, etc. For our purposes, this person would warm-up to a weight they either knew would be challenging for 6 reps, or a weight they thought would be challenging for 6 reps (depending on their experience). This persons’ numbers for 5 sets should look something like this – 230(6), 240(6), 245(6), 250 (5), 250 (4). For this workout, the goal is to train the squat at a given tempo, not to go for PB’s.
*Notice that once the top of the rep range was achieved, the load MUST INCREASE. When the top of the rep range is not achieved, then the load MUST STAY THE SAME for the next set. When the bottom of the rep range is not achieved, the load MUST STAY THE SAME for the next set (unless you are in warm-up, and you know you cannot do this weight for the rx’d reps once you have tried it for one or two reps). You MUST understand these principles, as progression is dependent upon this for this style of workout.

Repetitions – How should I progress if the workout calls for...?
Depends on the workout, for example:
Push Jerk, 5-5-5-5-5
In these workouts, you warm-up to challenging load for 5 reps of the given exercise. If you know your 1RM (repetition maximum) or 5RM for the Push Jerk, it will be easier. The reps could be any number with this style of workout, the rules will still apply. For this workout, you could have a loading sequence that looks like this for the Push Jerk workout – 145/150/155/160(4)/160. Each set has to be hard, with the next set being harder than the previous.
If the workout is:
Deadlift, 5-4-3-2-1
In this workout each set is VERY hard. You may even fail on a certain set, this is not a warm-up to try a 1 RM. A PB may occur with this, but each of the sets 5/4/3/2/1 should be maximal efforts for those sets. If your bestDeadlift is 400lbs, then your sets may look like 340(5)/350(4)/360(3)/375(2)/390(1).
If the workout is:
Press, 1 RM
You are being asked to find a 1RM, your best possible lift. Then you do not do gruelling sets leading up to this as you would with the previous workouts. If your PB is 160 for the Press, then your set scheme would look something like this, following a good warm-up – 95(5), 115(3), 135(1), 145(1), 155(1), 160(1), 162.5 (1), 165(f), 165(f). The goal is to get up to a heavy weight quickly, with the fewer sets the better, as for most people, this will allow lots of nervous system function for the important sets.

Sets – the ins & outs
Maintaining the correct rx’d tempo, and following the rules with the reps (see above), is imperative to getting the appropriate response from the workout. Progression from set to set, usually determined by load, is priority. However, when there is numerous sets prescribed within a workout for a given exercise, if you are using the correct methodology, then those muscle groups will be screaming for vengeance by the last set. And, depending on how you have been eating, sleep, relaxing, training, etc., can affect your performance on the latter sets. If you are to perform a Push Jerk WOD like the one above:
Push Jerk, 5-5-5-5-5
If your best 5 RM is 160 for the Push Jerk, then the optimal loading would be 145/150/155/160(4)/160. If the follow happens to your loading, 145/150(failed at 3)/150(failed at 2)/XXXXX. Then shut’er down there. You are not being productive. This is the point of Critical Drop-off.
If you are to perform the Press within an A1/A2/B1/B2 style workout, for 5 sets of 4-6 reps each set, and your best 6 RM Press is 130, then the following loading should occur – 120/125/127.5/130/132.5(4). If the following happens – 120/125(5)/125(3)/125(2)/XXXX. Then you are done after set 4, shut’er down. You DO NOT DO SET number 5. Arguably, you should stop after set 3.
These types of examples are specific to the Big Dawgs Blog, because if you are a true beginner to weightlifting, not just new to the Big Dawgs Blog, then you would not do what I had just said. You would just struggle through it, and move on. It will benefit this type of person, while it will only send the wrong training response to the more advanced trainee, and only be a hindrance to recovery. Although, going through the scenario will only benefit for later times. Being able to judge when the Critical Drop-off occurs may be difficult. It can depend on the order of your workout, and many other things...live and learn.

Pre-WOD Fueling rx’d
This is VERY individualized, VERY. Depends on your schedule, your digestion ability, the WOD, etc. But, for “general” purposes, I will give some scenarios.
A – your WOD is Fran (or any high power output/gassy WOD), and you are doing it at 5 pm. I would suggest eating your last meal around 1 pm to 2 pm at latest. Between this time, you only consume fluids (caffeine anyone?), and supplements if you so choose. You get to the gym at 4-4:30 pm, begin warm-up and anticipate the oncoming pain. The empty gut will benefit you immensely for these high power output WOD’s. Pretty much if the WOD is going to kick your ass, then you had better make sure that you are running light on the food (3hr+ post)and heavy on the motivation.
B – if you are doing the same WOD at 6 am. Wake-up, warm-up, and get’er done. Fluids, such as Ultima, or some kind of electrolyte may be beneficial to YOU. If you are eating, make sure it is not much more than what you could pick from your teeth following a handful of cashews, as it will only be coming right back up – if the WOD is done correctly. At this time, warm-up is even more important.
C – your WOD is Deadlift, 1-1-1-1-1-1-1. Bring your lunch pale and do as you please. Whether done in the AM/PM, eating food will not affect your performance, as this is a CNS WOD.
D – if the WOD is A1/A2/B1/B2 style, with short rest times, moderate (or more) amount of sets and reps, then you would want to follow the advice from Scenario’s A & B (shown above).

Scaling & Substitutions
The only WOD's that will need to be scaled are the ones in which there is a movement involved that has a progression. For example, a bench press does not have a progression, the weight just changes. A push-up has a progression. From kneeling to from toes. A deadlift does not have a progression, the weight just changes. A chin-up has a progression, from angled with a barbell, to assisted with weights or a band, to the free-weight version These type of movements may require a substitution.
Okay, so how do I scale or make subs?
Barbell's - If you only have access to DB's for the WOD, and if there is a rx'd weight for a certain exercise, use 66% of the weight in total - both DB's added together. Using DB's usually sucks much more.
Bench Press - If you do not have access to a bench press, then sub bar dips for rx'd reps. Ensure you are adding weight to your body if the bench press is being rx'd for loads (i.e. @ 30X0, 3-4 reps x 5 sets, rest 90 sec). This means failing at the top, or withing the rep range. See discussion on repetitions for more info on appropriate loading parameters. However, if you do not have access to either a bench or bar dips, use ring dips if you have them - same methods apply here. If you have none of the above try elevating your hands, either with paraletes (sp?) or weight plates, and maybe adding some weight to your torso if possible for extra resistance - as the point of this type of rx'd for the bench press is intensity in the pressing movement/musculature.
Box Jumps - Usually height will be the issue, so use a shorter one. If you don't have access to a box, try to measure off a distance about 75% of the rx'd box height from the top of you fingers when reaching overhead. Make a spot on the wall, or something, jump and touch it.
Chin-ups - Use an exercise band to assist you, or a machine if needed.
Chin-ups (strict) - Negative chin-ups for the same amount of reps are an option (4-5 sec lowering). If you can do them, but not as well as needed, then do what you can, but ensure you take your sweet time with the lowering portion, i.e. using a 50X0 tempo.
Chest to bar Chin-ups - Do regular kipping chin-ups if you cannot manage these in the rx'd quantity.
Dips - Use an exercise band to assist you, or a machine if needed. Do bar dips if you do not have rings.
Double Unders - There is no acceptable substitution, so stop reading the FAQ and learn Double Unders.
Front Squat - If you cannot do a front squat, do to flexibility, then become more flexible - simple. Also, sub back squats instead or DB squats.
GHD Machine - If you do not have access to a GHD machine, then you will not be able to do the GHD Sit-ups, or GHD Raises. Or, you may not even be able to perform the back extension, assuming you do not have a back extension machine either. In this case, you would either sub Knees to Elbows for the GHD Sit-ups, or anchored Sit-ups using a swiss ball - to allow full extension of the hips/spine. Sit-ups are too easy on the midline compared to a GHD Sit-up. The sub for GHD Raises would be negatives from a kneeling positon with your heels anchored. Going from an erect posture, control the lowering, to lying face down on the floor. Another possible sub would be a good morning with weight. Back Extension sub would be an unweighted good morning - hands behind head. Unless there is a weight rx'd for the back extension, in this case, you would have to hold the weight under you chin, or on your back.
Kettlebells - Use DB's of the same weight. 1 pood = 16 kg or app. 35 lbs.
Loads - This will likely be the most common substitution. When the load in a WOD is too heavy for you to use, or if that weight will make the WOD 2 times longer than it should, then the load should be reduced to a managable amount. Or if the WOD calls for unbroken reps, and you know that you cannot do that many reps at that weight for that movement - reduce it. Example - You are suppose to do Fran, and your best Front Squat is 100 lbs, then the 95 lb rx'd weight for males will not work for you. When Fran is rx'd on here, it is done for high intensity. But, if it is your first time with a WOD like Fran, and you want to use it as a benchmark, then go for it. But, there is a huge difference between doing Fran in more than 8 minutes with 95 lbs, and doing it under 4 minutes using 65 lbs. The under 4 minutes would be a better option. However, there are circumstances when you should grind through a WOD. Those kind of WOD's will probably assert themselves upon Coach's instructions, or just the layout of it.
L Pull-ups - Raise your knees until thighs are parallel to the floor, and hold this position. If possible try to keep your thighs at this position and extend your knees as much as possible. The issue will either be strength or flexibility, what is your issue? Work on it.
Muscle-ups - Substitite 3 Chest to Bar Chin-ups/3 Ring Dips per muscle-up. Or, 4 chin-ups/4 bar dips per muscle-up.
Overhead Squat - If you cannot do an overhead squat, do to flexibility, then become more flexible - simple. Also, sub back squats (as front squats will likely have the same problem as the overhead squat) instead, and practice HSPU's to develop OH strength/stamina.
Rowing - If there is no access to a rower, then run the same distance as rx'd. If you can't run or row, then do 10% of the rx'd distance for reps of a SDLHP (45 lb Barbell). So, for a 500m row, then you have to do 50 SDLHP with a 45 lb Barbell.
Running - If you live anywhere near Calgary, and it is winter, then you can probably forget about running. Unless it is indoor. Running is usually rx'd less in the winter anyway. However, if you are suppose to run for the WOD, and you just can't, then row the same distance if you have access. If you can't row, then sub 10 Box Jumps (20 inch/14 inch) for every 100m rx'd. If that is not possible, then sub 15 Double Unders for every 100m rx'd.
Wall Balls - If you don't have access to a medicine ball to do the wall balls, then do DB thrusters. Using the same amount of weight per hand as the rx'd weight for the wall balls.

Training Frequency, Double Days, Triple Days
For more on OPT Training Frequency - click here
Double Days & Triple Days - When these days are rx'd, they are done so for a reason. If you are a casual follower, and are into the Big Dawg WOD's for fun, that is fine. I would suggest trying one of the WOD's that would seem most beneficial for yourself, not all at once. Or, try to merge all of the WOD's into a single WOD. However, most people will not know how to do this, but try your best. Ask if needed.
For the serious followers, you know who you are. If you are intent on competing, then you had better plan out your days to get the best from the programming. Are you posting that you did WOD number one of the day, rested 10 minutes, then did WOD number 2? If so, you are not doing what is rx'd. You should be resting at least 4-6 hrs between these WOD's. I know circumstances may not permit this all the time, but try your best to do it this way. Resting between these WOD's gives your body time to recover enough to give a high output on the next WOD(s). Not resting the 4-6 hrs, ensures that you are giving 97% on each WOD, at best. Not the 100% needed to get you to the next level, which is the point of high volume training. You may think you are giving everything, but by consciously knowing you are doing another WOD in 10 minutes will not allow you to give your all - you just won't do it. Following the high volume weeks, the weeks with double/triple days, will be lower volume weeks, to allow optimal recovery, and subsequent performance improvement - greater work capacity across broad times and modal domains! So, hit the higher volume weeks hard, and as rx'd.

Running & Rowing percentages
If you do no know what it means to run or row at 80%, or 85%, for a certain distance then continue reading. If it says to run or row 400m, @ 90 % x 4, rest 2 min between, this means the times should be consistent. Not continuously slower and slower. You are being asked to show accuracy in your intensity of running or rowing effort. This will be much easier on a rower, as it gives second by second feedback. But, you should be able to know when you are running at a 1:15 400m pace, or running at a 1:20 400m pace - not kidding!
So, with that said, here are some "suggestions". If you are rx'd to run 400m @ 90%, and you know your best 400m run is 70 sec, then you should be aiming for 77-80 seconds. 80% would be approximately 90-95 sec. 70% would be approximately 100-105 sec. This would also fit for the same distance in rowing. These are very general suggestions, these % percentages will change based on your running skill and work capacity.
You are not taking a known time - your best 400m - and using math to get the answer. You are looking for a percentage of a known performance (intensity), a certain % of effort, not a certain % of time.