Depends on your level (beginner, intermediate, advanced), your age, how much sleep you get, how good your nutrition is, if you are bulking or cutting, what other stresses you have in your life, etc. Many of us prefer stimulating each major muscle group 3 times a week. Check out hte stickies or google Bil Star's 5x5 or Rippletoe's 5/3/1 for some ideas on routines and reps.