Set the pulley to roughly elbow height and stand side-on to the machine, elbow tucked against your ribs and bent to 90 degrees, forearm across your stomach holding the handle. Keeping your elbow pinned to your side, rotate your forearm outward and away from your body. Move only at the shoulder joint; your elbow shouldn't drift forward or back, and your torso shouldn't twist to help. Lower back to the start slowly rather than letting the cable snap your arm back across your body, since resisting that return is most of what makes this useful.