Trying to build your biceps? The password is "supination." That just means turning your wrists in toward your body. This is done at the top of exercises like dumbbell or cable curls.
Try it now with no weight. Hold up your arm in the top position of a dumbbell curl. Now watch your biceps and supinate. See your biceps contract harder and pop up?
Now do it weights. Before you start, try to touch your shoulder blades together – pull them back and down. This will help you keep your front delts out of the equation and keep more tension on the targeted muscle.