Stand up with your torso upright while holding a barbell at shoulder width with the elbows close to the torso. The palm of your hands should be facing down (pronated grip). This will be your starting position.
While holding the upper arms stationary, curl the weights while contracting the biceps as you breathe out. Only the forearms should move. Continue the movement until your biceps are fully contracted and the bar is at shoulder level. Hold the contracted position for a second as you squeeze the muscle.
Slowly begin to bring the bar back to starting position as your breathe in.
Repeat for the recommended amount of repetitions.
Variations: You can also perform this movement using an E-Z attachment hooked to a low pulley. This variation seems to really provide a good contraction at the top of the movement. You can also use an E-Z bar as well.