I suggest that you use a low bench when in the bent over position to rest your nonworking hand on, for better form and stability. Start with your upper body approximately parallel to the floor and your upper arm pressed tightly against it. Bring your forearm from a hanging position up until the triceps cramps in the back and you cannot extend your arm any farther. Bring the weight up with a little push, but no swing at all, and make double sure your arm is fully extended. This is the key point of the movement on which all your gains hinge.