What do you mean by wrists? Forearms or actual wrists? Doing wrist/forearm curls and reverse wrist curls are gonna build your forearms, which will help your bicep curls and most upper body exercises. If you mean your actual wrists, then theres nothing you can do bout that. Try using some straps. Whatever size your wrists are shouldnt stop you getting big arms. You may be using too much weight and just throwing it up. Try doing the same reps and weight your using now, but a lot slower and more control. Lock all your body up so all you use is your bi's. (stand with your back against a wall) If you dont make it, drop the weight.