There are numerous clinical studies that have found performing intense exercises works to stimulate energy expenditure and lipid oxidation for prolonged periods even after your workout is completed.  With intense physical exercise, your energy expenditure at resting pace also increases - meaning that you naturally burn more calories even at rest simply by performing intense exercises.
Your workouts do not need to be long, and should last around 30 to 40 minutes. Plan your workouts to perform three to four different exercises for each muscle group, and for each set, perform 6 to 8 reps. An example of a basic three day split workout routine looks something like this:
Squats 3 x 8
Leg press 3 x 6
Stiff leg dead lifts 3 x 8
Leg curls 3 x 8
Standing calf raises 3 x 15
Seated calf raises 3 x 12
Wednesday: Chest, Shoulders, Triceps
Bench press 3 x 6
Incline dumbbell press 3 x 6
Military press 3 x 6
Dumbbell side laterals 3 x 6
Close grip press 3 x 6
Triceps pushdowns 2 x 8
Friday: Back and Biceps
Dead lifts 3 x 6
Lat pull downs 3 x 8
Seated rows 3 x 6
Barbell curls 3 x 6
Dumbbell curls 3 x 6
Shrugs 3 x 8
The above is a very basic three day split, and works equally well for both men and women. Strength training just three times a week will help you build a little lean muscle mass, improve your strength and physical fitness, increase your metabolism, and help you burn off body fat easier to eventually get a flat tummy.
Ab Exercise for Flat Tummy
There are also plenty of abdominal exercises you can perform that specifically targets your abs and obliques. However, as we mentioned already, no amount of ab exercises will flatten your tummy. These exercises will strengthen and build up your stomach muscles, but you'll still not see them if they're covered up by a layer of belly fat. You need a combination of good diet and exercises to burn the fat off first. Regardless, below we have a quick ab workout that'll surely give your abdominals a good burn.
Abdominal crunches - start off with a set of basic ab crunches. With your feet flat on the floor, you can place your hands by your sides, or behind your head. You may find it helpful to have someone hold down your feet. Raise your shoulders and upper body off the floor using your ab muscles. Perform 20 reps.
Abdominal twists - those first 20 reps should give you a good warmup. Next you do some ab twists. In the same position, raise your shoulders of the ground except do it with a twist this time. Keep your hands behind your head. As you curl up, aim for your left knee with your right elbow, and aim your right knee with your left elbow. Perform 20 more reps alternating left and right sides.
Flutter Kick ab crunches - next, you kick it up a notch by performing flutter kick ab crunches (sometimes called abs scissors). It's similar to abdominal twists above, but tougher, and burns more. Keep your legs extended in front of you, raised above the floor by about 10 inches. Next you perform crunches just like abdominal twists above, except the difference here is that for each rep, you're also curling your knee up to meet your elbows half way. For each rep, curl your shoulders off the floor, and start off with twisting toward the left side with your right elbow curling up to meet your left knee. For the next rep, you curl up and twist to the right side, with your left elbow meeting your right knee. Alternate like this, performing 20 more reps. By now, your tummy should be burning pretty bad.
Lying Leg Raises - place your hands either at your side, or under your bum, and extend your legs fully in front of you without touching the floor. Raise your legs up to the top, and the lower it back down to starting position, without letting your feet touch the floor. Perform 30 reps.
Abdominal Tuck Crunches - still lying on your back, cross your arms in front of your chest, or behind your head. Bring your legs up, feet together, and with the bottom of your feet pointed towards the ceiling. Curl your shoulders off the floor towards your leg, and then back down to starting position. Perform another 20 reps.
There you have it, a total of 110 ab crunches that works you abdominal muscles for a fantastic burn; however, keep in mind that while this gives your ab muscles a nice burn, doing this does not burn your tummy fat away. You can do this once, or several times, depending on your level of fitness. Finally, remember that doing abdominal exercises is not the solution to flatten your tummy - for that to happen, you need a good diet, nutrition, and a entire body workout program that works to burn fat everywhere.