Face a cable machine with feet shoulder-width apart and with the machine pulley set all the way up.
Grab the handle with one hand and place yourself sufficiently far for the cable to be under tension when your arm is fully extended and relaxed.
While keeping your arm straight, push the handle down to bring your hand by your hips, then continue the circular motion towards the back and bring your hand up overhead, then forward to the starting position.
Also perform the movement in the other direction.
Either direction counts as one repetition.
Form tips
Keep your body facing the cable machine and don't arch or bend your back in any direction.