Exercises to help gain abs include static push-ups, which is like a normal push up, but you make no movement. There is also curl up heel taps start in crunch position, but curl up only a little and touch your heels alternating from left to right 20-30 taps, 3 sets.
Finally, double crunches by bring your knees to your elbows while crunching, 10 reps 3 sets. For details, visit http://www.menshealth.com/fitness/best-abs-workout-ever.
Lay on your back, raise head and feet slightly off the ground (8"-12") keeping feet together and hands just above hip... Try and hold this position for 1 min, after you can hold for a 1:30 then start holding a 10 lb weight over our abs with your elbows out. It may not feel like it's working right away but it is