1) Find the cable machine and attach a D-Handle attachment (the single arm attachment). Lower the cable pulley to the bottom.
Plant your feet firm on the ground with one leg in front of the other (use the opposite to the arm that you're training: left arm-right leg and right arm-left hand. Keep your knees slightly bent and your back straight.
Face away the cable machine. Do not completely extend your elbows and keep a slight bend.
Keep your arm slightly behind your torso - by keeping your upper part of your arm just behind your side.
2) Slowly curl the weight up by only moving your forearm and using your elbow. Do not move your shoulder and make sure that your arm stays behind your torso and you do not bring it forward.
Once your elbow reaches 90° squeeze the biceps.
3) Slowly lower the weight back to your starting position.