Incorporate these improvements and I guarantee your abs workout will produce fantastic results.
1. Don’t hold your breath:
Exhale completely and I mean completely as you crunch up…empty your stomach of all air as you come up and inhale deeply as you go down. This has a dual benefit. First you establish a rhythm in sync with your breathing and secondly the abs tighten and contract with not just the crunching up but also breathing out therefore making the muscles work harder.
2. Train lower back:
The erector spinae muscles are a set of muscles that run down the either side of the spine from the base of the skull to the pelvis. These are the opposing muscles to the abs. Training and stretching these will help you work your abs immensely. Try supermans.
3. Train all planes
In every abs workout make sure you train upper/lower and Obliques individually and separately. Best way to do this is as a circuit preferably twice a week.
4. Work upper Abs last
Most traditional abs exercises are upper-abs dominant. Start your abs workout with the lesser used and harder lower-abs exercises. The benefits will be immediate.
5. Use weights
Just like all muscles your abs also react best to increased resistance and become more pronounced and stronger. If you need to do 20-25 crunches to feel the pain add some weight like plate crunches, cable crunches etc, and watch those abs pop.
As an aside, for the adventurous, try the spiderman plank crunch. This one exercise works the entire core from all angles brilliantly.