2 Most Effective Exercises for a Flat Belly

Exercise 1.

Make a deep breath with your belly puffing out it as far as you can. Count one-two-three-four-five. Relax and exhale all air through your mouth. Draw your belly in pulling it towards the stomach. Imagine that you want to hide it under your ribs. Hold your breath. Count one-two-three and inhale again. 
Make number of repetitions equal to your age. If you cannot make all repetitions at once you can complete them later during the day.
This exercise can be performed when standing and sitting insensibly for people around you. Believe that it removes perfectly well fat from the belly and also massages the abdominal organs.

Exercise 2, "Angry cat". 

Stand on your knees, lean on palms. Make maximally deep breath draw your belly in under the ribs, arch your back up. Lower your head to the chest. Now you should be like a cat which suddenly met a dog. Hold your breath, count to eight, exhale and relax.
Return to your start position. Make three repetitions of this exercise.