It totally depends on what your going after... they are different stages to training...
If you are wanting to get more muscular endurance, not so much size, but good definition, you are in the stabilization stage... your going to want to do higher reps, lower weight and you are going to want to do exercises where you are having to stabilize... For instance, you could do curls while balancing on a bosu ball, or dumbbell presses while seated on a stability ball, etc... its a lot of core work and muscular endurance work... 3-4 sets of 12-15 reps... 60% of max weight...
If you are looking for maximum muscle growth, you want hypertrophy training... Higher weight, 80% of max, 10 rep sets... I do 4 sets of 10... 8-10 is about the average... This is how you will get maximal growth in your muscles...
If you are looking for power, you are looking at 3-4 reps, 90-95% of max and 5 sets on each exercise...
You need to be switching up your workouts every 6-8 weeks or your body is adapting and not getting to maximum potential...