Pacing yourself is the name of the game. Whether you have just started an exercise regimen, or been at it for a while, pay attention to your pace. If you are beginning a new health practice, make it relatively easy to manage - so you can keep on doing it! Don't press yourself too hard in the beginning - remember, you are building a habit. Likewise, when you have been doing something for a while, it's important to press yourself gradually further into it (increasing the pace), so that you stay interested.