If your objective is strength or power (think: heavy lifting), the textbook advice is to perform 3 to 5 sets of 2 to 6 reps per exercise. For hypertrophy (building muscle), the sweet spot is 3 to 4 sets of 6 to 12 reps. And if your objective is muscular endurance, shoot for 2 to 3 sets of 12 to 20 reps.