Contrary to popular belief, it is possible to change your metabolism, increasing the rate at which you burn calories. Three things will help you. Firstly, be sure to eat breakfast, as it gets your metabolism going right away. Next, try to be more active throughout the day. Try parking a few blocks away from your destination and walking the rest of the way. Finally, try to incorporate weight training into your fitness routine. Muscle tissue burns calories much more quickly than fat and by increasing your muscle mass, you will increase your metabolism.
One way to get the most out of your fitness routine is to be sure to feed your muscles carbohydrates and protein shortly after working out. This will ensure that your muscles are replenished and also that they are not sore for the next day. A good idea would be to keep an orange with you in your workout bag, and possibly a can of tuna fish once you are out of a public area.