My arms are my best body feature. Some people just don't seem to have the muscle bellies in their arms. I always had a bicep, even though I was a skinny kid, but some peoples arms seem to have little muscle on them. I am not sure how much arms rely on genetics, but I will tell you what works for me. Remember triceps make up almost 2/3 of your arm mass.
The KEY to getting the right muscles working is concentration. No not concentration curls, but really focusing on the muscle you are working and concentrating on using that muscle throught the lift. Its easy to use shoulders/back in curling exercises and even in triceps. Focus on squeezing that muscle and adjust whatever you have to, to envoke that muscle 100%.
Main exercises are nothing fancy:
EZ-Curl - I do one set with inside grip and two with outer grip. Sometimes I switch grips around and do two inside.
Straight BB curls - I do a couple sets of these and move my hand by about an inch or so from the first and second set.
Preacher curls - Usually 2 sets, sometimes i'll do one set with ez-curl inside grip and the other with dumbells. Be careful not to bounce the weight at the bottom, you can really do some damage. When you can't do anymore full reps, do half reps to really get the blood flowing.
You can throw in some cable curls on the preacher, or seated concentration curls in there. I don't do much else. Oh yeah, Use cheating to squeez out some extra reps!!!! The word cheat makes it sound like its something bad, well it isn't!! I see people do curls and they stop at the last rep they can do with perfect form. Thats bullshit!! I almost always will do one or two more reps by cheating as little as I can and still do the rep(arching your back, using momentum etc..), this is how I get the good pumps. If anyone tells you not to do that, tell them to take their arms and go clean out someones teeth. You have to be careful not to hurt yourself, but I never had a problem yet. I just can't stress enough on how important those last cheat reps are. If there is a secret I have to good biceps, thats it.