Supine Lying in a good alignment creates stability of the body in preparation for of arm elevation. Passive and/or active movement.

 Illustration by myself

Illustration by myself

Raising arms while the body is in an aligned posture.  The goal is to reach the floor with straightened arms.  One can start by touching the bolster with forearm while the shoulders are stable - retracted and planted on the floor/bed.  Removing the bolster when more range is achieved.