You should always use full range of motion but make sure that you never hyperextend your arms doing curls. Lock your elbows at your side the portion of your arm from the elbow down should be only portion that moves. Control both the concentric and the eccentric portions of the lift. When weight is at height of arc rotate wrist pinky side towards chest and squeeze as hard as you can and hold. I have always received max benefit from all exercises by doing drop sets and TUT training.