one of my biggest peeve's when i was a kid where my arms. they where pretty much the size of small twigs. not good. i worked at them for quite sometime untill i was able to reach 18" on the tape..probably a little too much considering the rest of my body was not at the same level. the first thing you have to remember is that 75% of the upper arm consits of the tricep. this is a large chunk and is very crucial to the look of a well built arm.
if you can, i suggest cable pullovers or skull crushers(laying on a bench with the bar over your head). these 2 exercises if done right should work the bottom portion of the tricep near the elbow. you want this to be filled in somewhat because it looks lanky if theres a big 'ol bone stickin out and the rest of the tricep sticks out like a freak. you have to lift big here. go at your own pace but add, add, ADD! the more weight you can do the better and bigger they will get.
the upper tricep or what i call the horseshoe needs to be worked as well. this gives you that hard ciggarette pack rolled in the sleve look. i actually use a machine to work these. sitting
tricep extensions, kinda like a preacher curl for triceps. again..big weight..keep adding..
now you need biceps too. big cherry poppers. preacher curl is always a good exercise. but standing curls WITH AN ISOLATOR BAR IS BETTER(piece that prevents the elbows from swinging back). underhand and overhand grips..the underhand grip will give you the inside of the bicep and the overhand will work the outside crest. remember BIG WEIGHT, the first few times should leave your arms like spagetti strings!
you really should work in some shoulder too. i do lateral lifts to work the peaks and back
cable pulldowns for the rear delts. you want to crown off the arm with a nice shoulder. i didnt do that at first and ended up haveing big lumber with no shoulder. didnt look too good.
dont forget your forarms. you might work them in regular exercises but it's a good idea to spend some time on these too. i use a machine at the gym but you can use dumbell rolls as well. nothing looks worse than a huge arm and a small forarm.. espesially when wearing a shirt that only exposes the forarm.
go pyramid style on your lifts..
example:
10X125
10X125
10X130
10X130
10X135
8X135
anyway..just ranting. just remember, it takes time. take a few snap shots of yourself now and go back to look at them in a few months to see progress. good luck!
edit..the last one WAS 8x315..haha..no way