Make sure you get plenty of both kinds of fibre - soluble and insoluble. Soluble fibre comes from things like fruit, while insoluble you get from whole grains. Keep your weight withing healthy ranges. Keep active. Watch your sugar intake. A low GI diet is very good, as you dont eat as much refined carbohydrates, and it is designed to release energy slowly.
By being physically active, eating lots of fiber, and cutting down on sugar.