Position ball comfortably at lower back.
Slide your butt down ball and towards feet to make easier as you go.
Pull the ribs down toward the hips squeezing the belly tightly.
Stabilize the neck and pelvis - this is the most common problem and makes you achy.
Avoid thrusting the body forward. The ball does not move.
The closer the buttocks are to the floor, the easier the crunch becomes along with the legs can help out more in balance.
The further away the hips are from the floor, the difficulty in the stomach gluts and neck increase. Use this to spot yourself.
Try holding your arms straightly over-head while squeezing ears (shown below).