Start with making a fist with both hands and folding your thumbs over your index (pointing) finger. Place your knuckles together in line with each other on a benchtop or bed. Lean you body over your hands and slowly start to straighten your elbow, keeping the back of your wrist down and thumb holding your fist closed. Hold for around 20sec and slowly shake your wrists off after.
Make sure you keep your bodyweight centres over your writs and keep your fists closed to get maximum effect / stretch