For this exercise start off with light weight on your dumbbells. You are going to keep a slight bend at the elbow throughout the movement.
Raise arms out to the side to about shoulder height. Hold for one second then raise further up overhead.
Return to shoulder height.
Then raise back up overhead.
After this slowly lower your arms down to the starting position.
The key to this exercise is to go very slow. If you moving with quick jerky motions lower the amount of weight you are using so that you can control the movement better.