The generalized rule for progression in my programs is as follows:
For a 4 week program
Week One: Go easy, make sure technique is correct, feel the movements, don't worry about weight and reps.
Week Two: Progress in either form, reps, or load. Oftentimes either load or reps as well as technique will improve. Leave a rep or two "in the tank".
Week Three: Further improvement in load or reps, possibly improvement in technique. Go hard.
Week Four: Go all out, reach failure on the top end set. Forced reps are great.
This basic progression can be stretched between cycles as short as 2-3 weeks (only for elite athletes)to as long as 12 weeks for newer athletes or athletes on a very light training schedule.
When you attempt progression by load or reps, I stress progression only on the top end set. If you try to progress on all of your worksets, you will often burn out early and be unable to increase on your later sets. The only time this doesn't apply is during a strip set(where you start with the heaviest weights and decrease weights from there) or with a wave/contrast set, (6/2/6/2 where you would attempt to increase on the 2nd 6 rep set and the 2nd 2 rep set).