These are the muscles that everyone wants to have. The legendary "six-pack"...the awesome abdominal wall...and for taller people, the oblique muscles, that girdle a human's sides, running down to the hip. On squat, fireplug guys like me who are short waisted, big obliques make me look too darned wide, so I don't work them too much...but I do work the hell out of my abs and I work them every day.
The first thing I did is to get lean. I got rid of all my fat. At the age of 62, this left a helluva lot of skin. I looked absolutely awful. I am getting rid of the skin slowly, by doing 200 to 300 reps on my abs every day.
One day, I do crunchies, hanging leg raises, and pull downs on the ab chair...On alternate days I do rope tucks and more crunchies. The idea is to isolate the muscles you are trying to work on, and burn them. The leg raises are good for the lower abs. My favorite over-all are the rope tucks. As the muscles grow, they become more noticable. I have a "4-pack" now, and need to really isolate the lower belly. Wearing a rubber belt, with velcro adjustments while working out, helps burn the fat off the lower belly.
Also, taking a fat burner at night...(a natural herbal one...NOT thermogenic), also keeps the metabolism burning fat, not muscle. Remember to eat every two hours, stay low on carbohydrates, and drink a lot of water. This keeps you clean, lean and mean! Remember, Rome wasn't built in a day...Abdominal muscles are hard work! Make sure you develop your lower back muscles, or you will be in for a strain...Core training is the basis of every other exercise...without core training, you are looking for injuries.