By and large, I've usually stuck with lower rep schemes (5-6 reps per set) for the compound movements, though on squats I have gone and still do go as high as 10 reps. When I've done direct arm "isolation" movements, I've tended to go to 12 reps. If you opt for lower (i.e., no less than 5) rep schemes, I think the key is to go all-out on each set, and as heavy as possible. This has worked well for me. BUT, that being said, not everybody gets the same benefits from the same training protocols. It's best, I think, to experiment with different protocols, keeping in mind that you need to stick with a given protocol for a decent amount of time to see the optimal gains you'd get from it. This takes time and patience, but it's worth it.