Focus on Quality, First and Foremost

Quality reps matter. Don't just move weight and shoot for specific rep numbers. Contract the muscles you're trying to use to move each rep. I give myself broad rep ranges so that I don't worry about focusing too much on specific numbers. I just want to get the most out of the targeted muscles from each rep.

For compound exercises, my goal rep range is usually 6-12 per set. When I'm able to get 12 reps for multiple sets, I know I can add weight next time.

For isolation exercises, my goal rep range is usually 10-15 or 12-20 reps per set (there are exceptions, like bicep curls where the goal is usually 6-12 reps per set). When multiple sets can be completed for the top end of the given rep range, I add a little weight the next time.

Easy does it. 

Focus and train with intensity.