1. Stand tall with your feet planted firmly on your workout mat
2. Bring your right arm across your body (you should have to have your bicep touching your chest)
3. Bring your left arm up and pin your right arm in place by pinning your left wrist against your right tricep
4. Hold the position to allow the full shoulder stretch
The primary muscles stretched in the Shoulder Stretch (arm across body) are the Shoulders and Traps.