find calorie/fitness calculator on the net, enter your stats, take 300-400 calories off that number and that's how much you need to lose weight.
5-8servings of fruit and veggies a day
8 glasses of water a day
5-6 small meals instead of 3 big ones (breakfast is the most important - make sure to get complex carbs like whole wheat bread, oatmeal, fruit etc)
4-6 times a week cardio for 30-50min, light weight training, many reps
no junk food, no sodas, no alcohol, no white flour (cakes, cookies, white bread, pasta etc.), nothing high in sugar (ice cream)

This has tips. Nourish your body thin, instead of starving your body fat. Good carbs like celery and carrots will never make you fat. Bad carbs like cake will, but you don't need to know the whole science of glycemic load. You need to re-learn how to eat so you can become thin and healthy. Salt has no calories but makes you fat and burning more calories does not help this fatness.
Find out about fastest way to lose weight, most effective exercise, good and bad fats, water retention and secret trick used by models to flatten their tummy before an event. Reading a book will take you hours but the information on a post, taking minutes to read, is not enough. The webpage below has just enough to know what you need to know. Links page has gov. BMI calculator to find out just how much overweight you are (teens plug in your age to compare to others your age).
You can force your body to lose weight with not enough calories, but if you continue it, you will starve to death. With an abundance of healthy foods, you lose weight just as fast, but only until you reach your ideal weight. You can continue eating this way the rest of your life and always be at your ideal weight.
http://www.phifoundation.org