do high intensity exercise 3 or 4 times a week. For instance repeat the following 8 times after selecting a good running track (could be a park or a track):
1. run as fast as you can for 30 sec.
2. Jog back to starting point at a very relaxed pace
3. Repeat (1 and 2) 8 times
It should increase your metabolism
and help you burn fat long after you have stopped exercising for the day.