First pin the pulley height to the highest position then pin a suitable lifting weight. One at a time, grab the cable handles in a palms up grip and position yourself in the centre of the cable rack.
Your core is tight, your feet are planted on the ground at shoulder-width and your arms are outstretched to the side of your body and parallel to the ground. This is your starting position.
Commence the movement by squeezing your biceps and curling the cable handles up from the elbow joint. The elbows should work like a hinge with the forearm being the only moving part - the upper arms remain stationary and parallel to the floor. Exhale through the movement.
When your biceps are at maximum contraction, squeeze for a second and then reverse the movement by extending the arms to the starting position, inhaling as you do.