Starting off, set the pulley arm to the lowest setting you can and attach a rope handle.
Your feet should be about shoulder width apart.
Then with your body straight (no bending of the back) grasp the handles and stretch them high overhead while at the same time spreading the rope handles as wide as you can. So you are pushing your arms up and out.
Return to the starting position by slowly controlling the lowering portion of the exercise, until you have lowered it as far as you can behind your back.
The key is on the lowering portion don't let the weight just jerk your arms back. Make sure you are in complete control and are slowly lowering the handles. If you can't maintain control properly, lower the amount of weight.