Personally, for me it's total muscle overload. I have to overtrain in order to grow. It would be nice for example to do a chest workout as follows;
incline bench, 3 sets x 8-12 reps.
Flat bench, 3 sets x 8-12 reps
dips, 3 sets x 10-12 reps
flyes, 3 sets x 12-15reps
Yeah, that may work for most people, but since i never had the genetics for muscle growth, I had to conduct studies on myself, my eating habits, and my training. Now since I'm tall (compared to 90% of the BBing world) and never had any muscle potential shown on my body, I figured I needed some extreme training, but not so much as that to make me really over train. So for the past month, this has been working for me;
Incline db presses, 3 sets x 6-10 reps
flat bench press, 3 sets x 6-10 reps
dips, 3 sets x 12 reps
hammer strength incline presses, 2 sets x 10-12 reps
hammer strength flat presses, 2 sets x 10-12 reps
cable crossovers, 3 sets x 12-15 reps
As u can see, I've added a little more work than I usually do, but this is the way I've found my larger muscle groups grow best. Heavy compound movements first, machines second, cables last.
Just like back, but I always save deadlifts for last cause I go so hard, I have nothing left after that. Also deadlifts drains U unlike any other exercise. Quick back example would be: Chins, BB rows, 1 arm db rows, 1 arm hammer strength machine rows, hammer strength lat pulls, cable pulldowns, and deadlifts.
I haven't found yet what works best for small body parts like arms, but I've been training to total muscle failure on them with moderate results. My damn arms are pretty long, so it's very tough.
It all depends on the individual. Maybe 12 reps works for some, but not for me. I've tried it for too long with no forward progress.