The quickest way to bigger arms is to train the triceps. They have greater growth capacity than the biceps. First, start using a closer grip on ALL of your bench pressing/OH pressing exercises. Do dips if your shoulders can tolerate them. In addition to this, hit your triceps twice a week. Pick a lying extension exercise like barbell extensions to the throat, chin, or forehead, or the various dumbell extensions. Do 3-4 sets of these and go heavy--6-8 repetitions. Next, do 2-3 sets of pushdowns for higher reps 10-15. Don't overtrain, 10 to 14 sets per week is enough for your tris. You must always try to improve, whether it be less rest between sets, more weight, or more reps, or all three. If you keep using the same weight, reps, etc. you won't grow. Use a similar method for biceps, but use less volume. The above worked(works) for me. Really, many different things will work; the most important factors are nutrition, regularity of training, intensity, and rest (oh, and genetics).