Here are a few basic stretching exercises:
Chest stretch: Place the palms of the hand on the back of the head and bring elbows to the back.
As a progression, place extended arm (s) against an open doorway and lean forward, creating a gentle tension across the chest
Arms across the chest: Facing forward, extend the right arm and draw across the chest. Arm should be as straight as possible with gentle tension developing across the right shoulder. Grasp right elbow with left hand. Apply gentle pressure with the left hand to increase tension on the right shoulder. Repeat with other arm/other side.