The secret to getting flat abs is to do the exercises correctly. That means that the abdominals have to be very pulled in. They cannot be allowed to bunch up and poof forward. When that happens, the rectus abdominis, the outermost muscle of the abdominal muscles, is getting shorter and bunching up. This might make that muscle stronger, but it will not result in balanced development, core strength, or a flat stomach (crunchers take note!). The flat abs come from the deep scoop of the abdominals, balanced by the length and breadth of the spine.
Warm Up: One of the keys to doing abdominal exercises effectively is being warmed up first. If you haven't warmed up yet, choose at least two exercise from the Warm Up Folder.
Return to this step-by-step for the first full-on abdominal exercise, The Hundred.