The biggest mistake people make when beginning a fitness program is pushing too hard, and then quitting. For general health, the Centers for Disease Control and Prevention recommend at least two and a half hours of aerobic exercise a week plus muscle strengthening at least twice a week. Aim for 30 to 45 minutes three times a week, and work your way up. According to Lazarre, a beginner’s program should look like this: 20 minutes on the treadmill (start out walking and build up to a light jog), plus 10 minutes on the elliptical trainer or bike, followed by 10 to 15 minutes of weight training. “Doing two types of cardio will help alleviate boredom and exercise different areas of the body,” he says.