I agree with most of what AllTheOtherKids said...except one thing. Crunches can and should be a part of your abs routine, however, you need to watch what you eat, and you need to do cardio at least three days a week. Firming up your abs should be part of an overall excercise plan that includes weight training.
Exercise- crunches, crunches, crunches! :) Also, try to eat more almonds, bananas, eggs, soy, apples, dark chocolate, peanut butter, leafy greens, yogurt, & avocados! Drink lots of waters to flush out toxins, and try to avoid sugars (candies, sodas, etc.) and exercise every day! Good luck :)