The diagonal shoulder abduction exercise is great for strengthening all of the muscles of the shoulder that help with posture and stability.
Stand tall with your feet hip width apart and your knees slightly bent.
You may also perform this exercise seated on a chair if you have poor balance or feel unsteady on your feet.
Start with your right hand down by your left hip with your thumb pointing down toward the floor.
With your elbow straight, lift your arm up and away from your body, in a slow, sweeping diagonal motion and then slowly return to the starting position.
When you begin the movement your thumb should be pointing down toward your left hip and as you come up, your arm will rotate so that your thumb points up and away from you.