im pretty much like madgame.. i approach gym with a set plan or at least an idea of how long i want to spend in the gym and the type of workout i am doing.
if u are bulking then its not too hard really. i mean u aren't gonna be running or working abs so that eliminates a lot of confusion..figure ur gonna do somewhere between 12-25 sets per muscle depending on how long uv been lifting.. i'd say 4 exercises, with 2-5 sets per exercise is good. if u feel u aren't working hard enough, then add weight while ur bulking..
its not so much time that is important, its more intensity and taking ur muscles to failure. for me it takes about 15-20 sets to totally fatigue a muscle group, but i have been lifting pretty seriously for a few years now.. so i am usually in and out in under an hour..