HOW: Get set-up laying on your side with your hips and knees slightly bent, you can use a pillow for head and neck support. You can rest your arm on your side before starting, the goal with this exercise is to try and keep your arm parallel to the ground. To start, point your thumb so that it is facing forward and slightly up towards the ceiling, maintain this position with a straight elbow, then lift your arm up into an overhead position that you feel comfortable with. Slowly lower down and repeat. Perform on both sides, you can use a light dumbbell once the weight of your arm is no longer challenging.
FEEL: You should feel the muscles on the outside and behind your shoulder working as well as your shoulder blade muscles.
COMPENSATION: Do nut shrug your shoulder, do not let your arm and hand rotate inward, do not rotate your body. Do not lose the plane of motion with this exercise, focus on keeping your arm parallel to the ground as best as you can.