try doing more sets, i do 12 sets on small bodyparts where as most ppl say only do 4, 6 at the most. though i have made great gains and i have always done this money sets, people respond differently. here is a sample routine i reccomend:
*seated preacher ez-bar curl (or standing barbell curl): 4 X 10, 8, 6, 4 (pyramid weight up each set)
*seated alternating dumbell curls: 3 X 10, 8, 6 (i pick a weight i can do around 10 reps for each arm and do as many reps as i can with this weight the first and second set, then on the last set i get the next heavier set of dumbells which is five up on each dumbeel in my gym and do as many as i can which is around 6 usually)
*concentration curls: 4 X 8-10 (finish workout off with a nice exercise to work the peak and just use the same weight and try to get 8-10, up weight whenever possible)
that is my favorite routine, try it if you want and see how it goes.