well your triceps are about 2/3's of your arm. Training them, your arm will grow faster than just hitting bi's. i used to hit them together, supersetting. Close grips, nose breakers, dips and rope work will give you a nice horseshoe and fill that back arm out. There's a ton of tricep exercises out there. I like doing pushups on a weight ball (diamond pushups) at the end to destroy my tris. Tris and bi's are relatively small muscles, you could hit them twice a week. Maybe after chest and then again on their own day.