Single Long Arm Opening Up
Set the cable at slightly higher than shoulder height. Grab the cable handle with one hand move back far enough that your arm can be straight with out touching the machine and the cable weight stack should be slightly lifted. Then angle your body 45 degrees away from the machine (so that you are turning into your outstretched arm. Keeping your arm straight, begin to open up your arm, pulling it away from the cable machine. Try to keep your shoulder pushed down away from your ear an see if you can feel your shoulder blade push back and sliding towards your spine. There will be a point where your arm will not go back and further, stop there, and try not to twist your body making it feel or look like you are getting further. Keep that body absolutely still. Take your time returning back to your starting point. Do 8 to 12 of these and make sure to repeat on the opposite side.
SPECIAL NOTE: For all the In the Gym: Cable and Dumbbell exercises pick a weight that you can do for 8 to 12 reps fairly comfortably and with perfect technique. After a couple of weeks of performing at this weight and with perfection, on then, move up to a slightly heavier weight that feels challenging once you get to that 8th or 12th rep. Once you feel absolutely confident in performing every rep with absolute perfection, only then, go to a heavier weight that is challenging you through out the set.