Start: Grab an EZ-curl bar with a full, overhand, shoulder-width grip, and stand with the barbell hanging in front of your thighs. Set your feet shoulder-width apart with your knees slightly bent, and lean forward very slightly at the hips. Pull in your abs and tighten all your upper body muscles, and slightly bend your elbows.
Finish: Raise the bar in front of your until your arms are parallel to the floor. Pause, then return to the starting position
Do the same movement while lying on a steeply inclined bench. You'll sacrifice range of motion but make the exercise much tougher.