1. Get in a half kneeling position. The leg that is closest to the cable machine should be placed forward, and you want to be in about a hip width stance.
2. Set the cable attachment so it is about chest height, grab the attachment with your outer hand (farthest away from cable machine), and lightly rest the fingertips of your inside hand on top of the other hand. This grip takes the inside arm out of the equation and really forces the core muscles to work much harder. When you extend your arms, the cable and your arms should form a 90 degree angle, so position your body accordingly.
3. As for your grip, I like to place the hands on top of each other as this makes the body more symmetrical. Placing one hand above (not on) the other causes one arm and shoulder to be slightly higher than the other, and I'm not a fan of this.
4. As you extend your arms, take a deep breath out, actively tuck your rib cage towards your anterior pelvis, brace your core, and lightly engage your glutes. Hold your arms in the extended position for 1-2 seconds before you bring them back to the starting position.
5. As you bring your arms back in towards your body, stop when your elbows touch your sides. Don't allow your hands or forearms to touch your anterior core. Many people make this mistake.
6. Relax your arms so they do not dominate the exercise.
7. Keep your shoulders pinned, and your shoulder blades retracted and depressed (together and down towards your opposite hip). Do not allow yours shoulders to round or shrug.
8. Maintain a tripod foot (weight on the mid to back of your foot, and keep your big and baby toe down) for the duration of the exercise. This will dramatically improve your overall stability and ability to perform this exercise. You might even feel the glute of the forward leg, and this is a good thing.
9. Maintain proper alignment for the duration of the exercise. There should be no rotation occurring in your shoulders, torso or pelvis, and your body should not tilt laterally. It is very common for a person to compensate for lack of core stability by leaning their shoulders, torso and pelvis, away from the cable machine (site of the attachment). Your body should remain relatively vertical (can have a slight forward lean in your torso), and your spine should remain in a neutral position.
10. Do not allow your knee to deviate medially or laterally.
11. Reset before each rep.
12. Choose a weight/band resistance that allows you to accomplish the above.
13. You can also perform this exercise with a resistance band.