Stand up straight with the side you would like to stretch sideways to a door.
Reach the arm closest to the door forwards and grasp the door frame around chest level.
Your arm should rotate inwards so that your thumb points down.
Keeping your arm straight, step your body round to face the door.
Do not allow your shoulder to hunch or your body to lean.
You should feel a stretch across your upper back and perhaps the back of your arm.
Hold this position, using your breathing to relax into the stretch.