Pull your elbows up and out. Keep A 90 degree angle at the elbows and rotate your hands back. Pinch your shoulder blades together and down in the top and release them as your hands go back to the start position.
These are a great warm up in a group setting just have everyone grab a pair of 2.5, 5 or 10lb plates and do 2-3 sets of 20. You can also do them towards the end of the workout as a shoulder prefab movement.