double your heart rate for 20 minutes every day. As you get fitter, it will take more effort to do this, whether that effort displays itself by running faster, or by running further. As you'll learn form the link provided above, it's best to do both.
Further, do gravity-resistance training (what we old guys used to call weight lifting). The more muscle tissue you carry on your frame, the higher your metabolism is, and the more fat your body burns to feed that muscle.
I'd suggest finding a half-hour to an hour twice a day to do both types of PT. Run in the mornings, lift heavy stuff in the evening, or vice versa.
Eat right, but don't get too caught up in the hype about any 'super-duper special diet'. Eat properly, lots of meat, veggies, cereals, and leave the fast food/junk food alone. Booze is NOT your friend when trying to lose fat and gain muscle.
Or you can just drink a lot of coffee, dip Cope, and smoke heavily. This'll boost your metabolism as well. ;D
Read the link, and good luck.