This is a very advanced exercise used mostly by body builders and power lifters. This exercise should no be done by beginners and it is recommended that someone demonstrate this exercise you and spot you while performing it.
Steps
Lie flat on a bench with your feet placed firmly on the floor and your abs drawn in.
Grasp the dumbbell in one hand and bring it up to the side of your chest, this is starting position.
Extend your arm, pressing the dumbbell up till your arm is straight and your elbow locked.
Using slow controlled movements, lower the weight to starting position.
Switch arms after completing reps with one arm.
Tips
This is an exercise which can help you strengthen the muscles of the Rotator Cuff, which support your shoulder.