Its very important that you keep your body and elbows fixed in place throughout the set. Do not move your elbows! Focus on only allowing your forearms to move.
This is an isolation exercises, so your focus should be on muscle contraction and stretch - not on the weight.
Instructions
For the standing high pulley cable curl you'll need a cable machine with two high pulley cable attachments. Set up by attaching a single grip handle to each of the high pulley cables and selecting the weight you want to use on the stack.
Grip each of the cables with an underhand grip (palms facing up) and stand in the center with your arms outstretched. This is the starting position.
Keeping your upper arms and body fixed, curl the handles in towards your body as far as possible.
Pause, and then slowly lower the weight back to the starting position.