Someone else correct me if I'm wrong, but I've always heard/read with weights that if you do fewer reps of heavier weights, you bulk up more, whereas more reps of lower weight builds leaner muscle. I do 3 sets of 10, 3x a week. I hear some people do even less, like 3 sets of 7 with as much weight as they can do and complete the reps keeping proper form.
Be sure you adjust diet properly too. You 'injure' your muscles during workout and the body repairs them afterwards. You've got to fuel that process. I'm not an expert on that area so I won't try to say too much. I generally try to eat a higher protein, lower fat diet. I've begun drinking a protein shake about 30 min. after my workout and have noticed a little improvement (I'm trying to bulk up as well).