Start lying with the band directly lateral to the shoulder and so there is tension when the arm is out at 90 degrees abduction range. (it's not slack). Have you arm to the palm is facing up. Pull the band down and outwards then down to your side using the muscles under your arm pit. Slowly then raise your arm up over your head in a outwards abduction arc, letting the band take the load of your arm to 90 degrees, Then lift your arm and hand above your head as far as you can go. Back sure for the first part of the movement your shoulder blade stays down, and then rises once your hand is in line with your head and you make sure your scapula elevates, abducts and rotates with the arm.