First, try a round back exercise. Sit on a folded towel with your shoulder blades against the wall, then scoot down so that your back is rounded. Fingertips should be pressing into the floor right by your hips, and your knees bent. Use your abs to lift your feet off the floor, straightening your legs up to the ceiling with beautifully pointed toes. Do 10-12 pulses in, trying to keep the legs as straight as possible. Exhale on each pulse. Do this 3 times.
Next, try a flat back exercise. This time, you want your back to be as flat as a board. Sit against a wall, and make sure your hips are pressed all the way back. Your knees should be bent and slightly wider than hips distance. Place your fingertips on the floor between legs, and lift your legs off the floor a few inches as you press your fingers firmly into the floor. Pulse up 10-12 times, exhaling on your lifts. To make it more difficult, extend your legs out to straight and continue. You can also lift and lower the left leg, then switch to the right as an alternative. Do this set 3 times, and be amazed at the strength your abs will gain!