Stand up straight with your arms by your side.
Ensure your palms face towards one another, with your thumb leading the movement.
Squeeze your arm gently into your side, and then continue with moving your arm directly forwards and up towards the ceiling.
Imagine you are drawing a "J" with your upper arm.
Ensure you lead the movement with your thumb in front.
Control the movement as you reverse the action, lowering your arm back down to the starting position.