When you are doing your ab work do you think about your breathing? Did you know that the proper breathing technique will help you develop that 6 pack?
When most people preform ab exercises they have a lot of air in their lungs. This prevents their abs from fully contracting because the air acts like a cushion.
To help develop your abs you want to breathe in at the start of the movement (crunches, sit-ups, leg raises etc) and breathe out as you contract your abs. This will help remove the oxygen from your stomach allowing you to get contraction of your abs.
Give this a try the next time you do abs!