depends how serious you are. You mostly talking about weight lifting right? if your going the clean way then you should use creatine or NO also make sure to always have your protein drinks, thats what iv been doing for a while, i really stepped up my weight lifting the past 6 months and am seeing a lot more mass and am always increasing the weight. for mma it is mainly eating well and avoiding processed foods.
if you know your kinetic linking then it is easy to see why your legs, back and shoulders are the most important muscles to train. you get most of you power from your punches from your shoulders and legs, your kick from your legs, and having a strong back really helps in the takedown game.