Below is the correct way to do a Crunch, watch the video below.
1. Lie flat on your back and bend your knees about 60 degrees.
2. Keep your feet flat on the floor and place your hands loosely behind your head.
3. This will be your starting position.
4. Now curl up and bring your right elbow and shoulder across your body while bring your left knee in toward your left shoulder at the same time.