1) Put one leg up on a flat bench - the opposite to the arm that you're working. Lean over the bench and put your other arm on top of the bench for support. Keep a bit of an arched back and keep your neck and spine aligned.
Keep a slight bend in your knee on the leg that is not on the bench.
2) Bring your elbow up so that your arm is parallel to the ground whilst holding the dumbbell and your elbow forms a 90° angle.
3) Exhale as you kick back the weight - extend your elbow so you lift the weight. Make sure that you are only moving your elbow joint. Go all the way until your elbow is fully extended.
4) Inhale as you bring the weight back to your starting position. Complete the repetitions on one arm and then swap to the other.