Not only do you want to exercise intensely and incorporate ab contractions throughout your workouts, but understand that your eating regimen is key in developing and losing fat in your midsection. Cut down on starches (simple sugars), especially at night.
These trigger the release of insulin, which increase fat storage.
*If you exercise before breakfast...this forces the body to use stored fat as fuel. **If you exercise after dinner...you will use circulating sugar and will burn more fat at night. Lift weights to increase muscle mass and speed your metabolism. Try to eat several small meals during the day....it takes energy to digest food.
The most important principle of fat control...take in fewer calories than you use.
PLEASE KEEP IN MIND, that if you train intensely your body needs food for fuel, so don't cut your calories too much on the days that you train hard. Pay attention to your body....your body will let you know if you need more calories (ex: by a decrease in energy and performance and a lack in toning/building lean muscle mass). Remember, if you don't cut weight gradually....you will lose too much muscle mass.
ACSM Health Fitness J., 5: 9-14, 2001.