When exercising on a program, it's best to mix it up each time. Doing the same exercises all the time can get your metabolism used to it, and it won't burn as much fat nor build lean muscle. Keep your body guessing!
Example: On Mondays, I strength train my chest, shoulders, and triceps. This week, I do Bench press and cable cross over for my chest. The following monday, I'll do either a decline bench and dumbbell flyes, or Incline bench and dumbbell presses. Never do the same exercise twice in a row.