Scapular retraction supine arm circles with weight (Scapular retraction stabilization, arm circles, with weight, supine)

Lie on your back and flatten your shoulder blades against the floor.
Hold a weight in your weaker hand.
Whilst keeping your shoulder blades still, slowly lift your weaker arm up, leading the movement with your thumb.
Keep your elbow straight and point your arm straight up towards the ceiling.
Holding this position, slowly move your arm around in small circles whilst keeping your shoulder blade still.
As this gets easier, try and move your arm in larger circles.