lots of exercise and eating healthy! you should probably exercise every day or every second day, maybe get your self into a routine or get an exercise plan!
maybe in the afternoons you could go for a 20 minute run around the block, then when you get back you could do a bunch of sits ups and push ups. set your self lots of goals (e.g. do 30 sit ups and push ups a day) and perhaps when you've lost a certain amount of weight that your happy with, treat yourself with take away or a cupcake or something! but don't get into a habit of eating lots of junk food!
good luck :)