I've always walked the rack. If I get the 12-14 reps, I move up just a bit and see if I can get the 14 reps again. We used to say "We're getting stronger 2.5 pounds at a time." When I get to failure in a 12 rep set, that's my heaviest set. I usually do 6 sets for an exercise, first set is a warm up, then good 4 working sets, then the last set is a just a bit lighter than my heaviest weight to get the 14 reps again. A problem in my gym is that they do not have the half number range of dumbbells (22.5, 27.5, 32.5 etc.), so doing a smaller muscle like biceps or delts, it sometimes not feasible to increase a full 5 lbs. I requested these dumbbells, but they have not appeared yet. I find this to be very limiting, and almost worth changing gyms. In this case, I sometimes move to the cables where I can hang a 2.5 pound plate on the pin to get the weight I need. You do what you have to, improvise at times, to make gains.