Its a trial and error process to figure out what will work best. I used to train with a guy and he responded best to lifting 6 days a week, hitting each body part twice a week. I've tried everthing: the push/pull routines, high volume routines, three days a week, four days a week. For me, I've found that I respond best to five days a week on a High Intensity Training routine. My days are divided into: Chest, Back, Legs, Shoulders/Traps, and Bi's/Tri's/Forearms, with abs four times a week.