Do you want to get big? Then train heavy enough that you can do 10-15 reps with good form.
Do you want explosive strength for sports? Then look for around 15-20 reps but do the pushing part explosively.
Do you want to get strong? Lift heavy. Do 5 sets of a weight you can lift for 5-8 reps.
Going for endurance? Then you're looking for weights that take you to 30-50 reps.
Adjust the weights if you're not in your rep range, and don't cheat. Rest longer between sets if they start dropping off.