Here is what I've been doing for what it's worth. Since I have just started to lift again (early April) I am only doing skullcrushers and pulley pushdowns, Doing 8-10 reps for 3 sets each and when I can get 10 reps on all three sets I increase the weight a bit. I have started to take the last set to failure. On the pulley pushdowns I immediately drop the weight (easy to do on the pulley system) and do more reps to failure and then drop one more time. Even though I've lost ~30# my arms have grown about 3/4 inch most of which has been the tricep.