As a personal trainer, I can tell you that they are all important. Legs provide the foundation for your stance, strong/enduring legs will keep you planted. The abdominals and low back musculature is important to support the upper body and keep it stable against recoil. Chest, back, front shoulders, mid shoulders and rear shoulders support the gun. Working triceps and biceps wouldn't hurt either. There is probably no need for wrist work unless they are weak or you are shooting a major caliber. I find the slower I do exercises(like a moving isometric), I am better at the range in terms of static position(only trigger finger moves). Standing exercises will probably transfer best. Front and side raises for shoulders will make a difference for shooting. If you any other questions, let me know.