Its very important that your hands do not go higher than your elbows. To prevent this from happening, as you raise the dumbbells up, tilt them forward as if you were pouring a jug of water.
Always do this exercise slowly. Its an isolation exercise and the focus should be on working the muscle correctly - not moving as much weight as you can.
Dont bring your arms up too high - up to shoulder height is far enough.
Keep your core tight throughout the exercise. This will help with stability and ensure that your abdominal muscles and core strength are benefited greatly.
Instructions
Grab a pair of dumbbells and sit up straight with your feet around shoulder width apart on the center of an exercise ball.
Hold the dumbbells down at your sides with your palms facing in. Hold the dumbbells out at around 4 inches from your body. keep your back straight and your core tight. This is the starting position for the exercise.
Keeping your body still, eyes facing forward, with a slight bend in you arms, slowly raise the dumbbells up to around shoulder height.
Pause, and then slowly lower the dumbbells back to the starting position.