HOW: Begin in a sidelying position with a dumbbell or kettlebell in hand. Prop yourself up with your elbow underneath your shoulder. Push through the forearm to lift the torso away from the ground. With the arm rotated away from the body,, press the weight vertical towards the sky. Slowly lower back down to the torso.
FEEL: You should feel the outside of the shoulders working at the rotator cuff. You should feel the inner shoulder blades working at the middle trapezius.
COMPENSATION: Avoid shrugging the shoulder. Avoid letting the arm go behind the body.