If there are four essential disciplines to maintaining top level physical health, I would list:
1. Eat an apple a day. Everyday. It makes a difference.
2. Drink at least 64 ounces of water or juices per day. Hydration is nonnegotiable. Just do it.
3. Do 25 to 250 push ups everyday. You will see the positive impact.
4. Sleep 6-8 hours per night. Uninterrupted, quality sleep. It will recharge your batteries.
If one is uncompromising about these four disciplines, he or she will also prioritize the many other healthy-living habits.