STARTING POSITION:
Select the appropriate weight of the dumbbell. Lie on a fitball on your right side, it should be under your right ribs. Your feet should be touching the floor. Place the elbow close to the body and let the dumbbell hang in front of you with your forearm perpendicular to the floor. Retract your shoulder blade.
MOVEMENT:
Maintaining the elbow close to your body, do an external rotation to lift the dumbbell as high as you can. Return to the starting position with a smooth movement while you inhale. Repeat the movement for the specified amount of repetitions and then switch sides and repeat with the other arm.
TIPS: While your are doing the exercise, move only the arms, make sure you don't move any other part of your body. The exercise key is quality over quantity. The trick is to perform the exercise using proper form.