Stop smoking is the first step. There is no need to wait till your in shape to start training. Find a good instructor and start training. One hour of MA training will burn more calories than 1 hr of high impact aerobics. Even if you don't start training now, do something active. At your age you may not need a strict diet. Eat healthier, cut out the McDonalds and some of the other junk food you may be eating often. Your still young and your body is still changing. You should get into the habit of working out now. Just remember in order to loose weight you need to take in less calories than your daily needs and more than your resting metabolic rate. This with exercise will cause you to loose weight. You must eat properly though. Eating 5 smaller meals a day spread out about 3 hours apart will help you maintain your blood sugar levels. You need to maintain your blood sugar levels in order for your body to take nutrients from fat and not lean muscle. Basically if your eating one meal a day while working out you may be getting the calorie levels you need but your hurting yourself in the long run.