Years ago it was suggested to me to place my hand as high as I could on the side frame of the door, walk my fingers upward until I got a good stretch, lean into it a bit, hold briefly. Do this every day, maybe several times.
How I wish I had listened, been more diligent. My right shoulder is frozen. Intense msasage is helping a little bit but I'll be seeing an orthopedist soon and likely starting physical therapy.
Jan in VA