Diet: Eat no more than 1,500 calories a day. Eat healthily. Avoid junk,processed, and sugary foods. The more organic the better. Lots of fruits and veggies + portion size protein (food pyramid).
Lifestyle: Stay away from drugs. Have good hygiene; brush your teeth and shower often. Get 30 mins of active exercise each day at a minimum. Play a sport or go to the gym.
Get enough sleep, at least 8 hours a night. Avoid caffeine (stuff like coffee and Red Bull).