I did 2 sets of some exercises, 1 set of others (namely squat and DL), 3X a week.
My first cycle I basically followed the plan laid out on the site.
The weight progression is based on the concept of progressive load. Basically here's how it is: initially your muscle is deconditioned, you apply a load (a load anywhere from your 20 RM to your 1RM can produce hypertrophy), your muscle becomes conditioned to that load, in order for more hypertrophy, you need to increase the load. The level of conditioning your muscle is at is inverseley proportional to the amount of microtrauma you will incur by exercising.
With HST, you are constantly increasing the load by adding increments each workout. This maximizes the potential for hypertrophy, by maximizing the microtrauma. The standard size for an increment is 5% of your 5RM for the exercise BTW.
The matter of conditioning brings us to the concept of SD, the need to decondition a muscle to resensitize it to lower weights so that the progression of weights may start over, and you may once again milk your muscles for all the microtrauma they're worth.
I suggest you do some reading in the articles section and on their forum. The FAQ is a great source for scientific info related to BB, regardless of training method. Although, once you get a grasp of all the concepts, HST just seems a natural choice. That's what I like about HST, Bryan takes a very no BS approach, not using any buzz words like "shock".
Good luck man!