Warnock -
My approach is to keep my body guessing so it never gets used to doing the same type of thing. So each week I have a different theme for the weight and reps I'm doing.
One week it may do a 5 or 3 rep max similar to what Stevo suggested, next week I might do a bodyweight week so high rep but much lower weight, next week superslow reps at 70%, next week Tabata sets. etc
No pattern to it just decide at start of week what your going to do, so many variations out there. It keeps going to the gym interesting as well because your not getting bored doing the same stuff.