Time Management. While six pack abs might be a top priority as a teen, it's also important to work hard academically. The CDC recommends 1hr of physical activity per day which will help strengthen a teen's bones, heart, lungs, muscles, and it will help reduce depression and stress. After coming home from school, teens can set aside an hour of time to exercise before starting (or as a break from) homework.
Balance. Daily exercise is important for both physical wellbeing and academic success. Don't forget to eat balanced meals and healthy snacks (check out the myplate recommendations). If you are into competitive sports avoid fad diets, supplements and steroids. Organize your time so you can get homework done, take good care of your body and don't forget to have fun!