Start on your hands and knees, with your hands under your shoulders and knees under your hips.
Take one hand off the floor and reach in and through between your other arm and your legs.
Allow your body and head to follow, moving your shoulder down towards the floor as your hand reaches through.
You should feel a stretch down your side, shoulder blade and neck.
Take your upper arm and reach it up towards the ceiling, following the movement with your gaze.
Hold this position, before reversing the steps to come out of this stretch.