The first way is simple in theory, but hard in practice. Eat less! If you're at a stable weight eating 2000 calories daily, you will need to eat 1500 calories daily to lose weight. By eating 500 fewer calories each day, you will burn about one pound of fat each week. A high protein, low carbohydrate, moderate fat diet is an excellent way to burn fat in a healthy, muscle-sparing way. Eat three small meals with one or two high protein snacks spread throughout the day. You'll maintain your energy levels without feeling "starved." A more severe calorie reduction will lead to muscle breakdown, slowed metabolism, fatigue and quitting your diet early.
Second, burn more calories by increasing your metabolism. Both cardiovascular exercises and weightlifting are recommended. You can easily double or triple your metabolic rate during simple exercises. By increasing your muscle mass with weight lifting, you can increase your resting metabolism as well. Your body burns more calories to maintain 10 pounds of muscle than 10 pounds of fat. That's why bodybuilders need such large amounts of calories to maintain their weight, even when they're not working out.
Many fad diets promise amazing results in a short time. Don't be fooled. You cannot safely burn more than 1-2 pounds of fat a week. More weight loss than this is a result of muscle or water loss. On a fad diet you will tire easily, lack strength and endurance, have poor muscle tone, and notice sagging skin. Worst of all, when the fad diet is over, the weight returns.
Remember, the secret to healthy dieting is burning fat, not just losing weight.