First, your medical history is very important.  If you have arthritis, high blood pressure, previous heart conditions, obesity, or diabetes to name a few, there are specific contraindications. The exercises must be appropriate in type, intensity, duration, and frequency. For example, someone with a heart condition must know the appropriate target heart rate.  Second, the exercises should be enjoyable.  You will be less likely to maintain a regular exercise program if the exercises are not enjoyable.  Third, the exercises must meet the end goal.  For example, if your goal is to become stronger in your upper body, having a program that focuses mainly on endurance is not going to be effective in reaching your goals.  Fourth, the exercises must fit into your schedule.  If you only have 30-45 minutes per day to exercise, the program should fit into that time frame.  You will be less likely to stick with a program if it exceeds the time restraints of your schedule.  Along with the issue of time, the exercises should be very convenient.  If you have a membership with a fitness center, it should be convenient.  Research shows that convenience is one of the top reasons why people either stop or maintain an exercise program.