If you were to trust one entity with your health, it would probably be the CDC. At their website, they offer some fundamental guidelines to keep you safe and prospering for years to come.
CDSee How Healthy You Are
Fruits, vegetables, and grains are all your friend. Fatty foods and drinks (that includes you, alcohol) should be taken in moderation and as part of a balanced diet. It is encouraged to get kids and teenagers physically active for an hour a day, whereas adults should try to get active at least 2 ½ hours a week. Do the stuff that gets your heart rate up, but also the stuff that strengthens your muscles. Such activities maintain your weight, reduce blood pressure, and ward off any number of ailments. Get checkups and ask your doctor what types of things could specifically improve your health. As for your brain, snatch seven to nine hours of sleep a night, and surround yourself with family and friends who can support you. A healthy body is wasted without a healthy mind to go with it.
You can read more in-depth recommendations here: http://www.cdc.gov/family/tips/