Checking in with your doctor before you start a new fitness regimen is a vital first step. Assess your health and fitness level so you can plan a workout schedule that includes the amounts of aerobic and anaerobic exercise you need. Next, find the activities that you enjoy the most. Your workout should be as enjoyable as possible--that's the best way to ensure that you will stick with your plan. Finally, be sure that you increase the level of intensity in your exercises as you get more fit. Challenge yourself!