Every little bit helps. Start by drinking more water, and NEVER drink soda. Walk, jog, buy a bike. If you're embarrassed to exercise in public right now, then you can do situps and calisthenics in your room. Eat plenty of fruits and vegetables. Don't starve yourself. That's a common mistake. You have to eat 4 to 5 times a day, but eat healthy foods and keep the portion sizes small. Stand up, turn around, pick up your chair, and hold it there for as long as you can. Every little bit helps.