for growth in the overall arm diameter, you need to be training your triceps first. its a bigger muscle, and consists of three muscle heads, instead of two. a human arm in perfect proportion would be something like 2/3 tricep and 1/3 bicep. rarely is this the case though...most often its half and half half. and id say that you see more guys with a little bit more size on their biceps than their triceps than you do who have larger triceps than biceps.
for myself; two handed over head dumbell extensions are really good. so are reverse grip rope pull downs for triceps. and for biceps, i respond really well to heavy precher curls, going as high as i can with pretty good form for about 8 reps per set. 4 sets. because of the arm pad, and the seated positioning...it really kills the bicep...takes the front delt out of the movement completely. with standing barbell curls you can use more weight, but almost alsways whats happeninig is your front dets are taking the brunt of the load.