Eazy Tip!
 

When performing concentration curls, avoid the tendency to roll your arms up your thigh, which makes the movement easier. Keep your arm perpendicular to the floor! Dont lock out and keep full tension on the bi's at all times.

and if u also cock ur hand back as far as comfortably possible and hold in tht position,, ull be creating a stronger contraction for ur biceps mainly the short head.. which is the peak on the bicep..