A: You do one set to positive failure, to prime your nervous system for optimal firing with a heavy weight. Rest about two to three minutes if it’s a big compound exercise (multi-joint; rest a little less on isolation moves), then perform a second set to nervous system exhaustion with X Reps added to the end—no break; as soon as you can’t do another full-range rep, move to the X spot and crank out partials for max growth stimulation. Your second set, with X Reps, is the money set—that’s where you’ll get the most mass stimulation for your efforts. You’ll feel it happening, believe us!
That being said, we have had reports of great success from some trainees who are doing X Reps on the first set and then using the second as a burnout set with less weight. You may want to experiment with that method as well.