A fairly lightweight stretchy band works best for this shoulder mobility movement. This activates the shoulder from all different directions. The main thing here is to keep the elbows straight. To help you remember the pattern in which I use in the video, I tell a story...

We are in math class doing subtraction and multiplication. We are bored so we fantasize flying over the rainbow. On the other side of the rainbow, I make a new friend and we bear hug and chest bump. Your new bestie and you go travel half way around the world together.