The reasons for wanting big arms are many and obvious. Arms rank second to a flat stomach as the most noticed and sought after fitness goal. The vast majority of people make three consistent mistakes in training for big arms. Depending on your current size (smaller arms will obviously respond more) my workout can add up to an inch in the first month and will continue adding size after that.
First, all workout plans should be well rounded and full body in focus. So if you are relatively new to training focusing on your arms is a mistake. Your primary goal in the early stages of a mass gaining plan should be the big muscles. Focus on compound exercises (bench, military, and leg presses, seated rows and lat pull downs in particular) that work the smaller muscles as well as the large. But if you have a foundation of training already (at least 6 months) then you are ready to isolate and can start seeing some real gains.
Secondly, did you know that the triceps muscle makes up 60% of your arm size? People who focus on bicep curls as the basis for getting big arms are completely wrong. The primary focus should be on the triceps, if overall size and arm balance are your goals (and it should be). Lastly, the mass gaining principals for arms are the same as for any other body part. You must go heavy and low rep. And I mean heavy. Most people grab up a set of dumbbells and knock out 3 sets of 12-16 reps of curls and wonder why my arms arent growing.
Here are the basic principals to remember in an arm workout geared to mass gains:
1) You must have a foundation of training before you start isolating arms
2) Do 3 triceps exercises for every 2 bicep exercise
3) If you can do more than 6 reps of anything with good form it isnt heavy enough
4) Never do the same number of reps with the same amount of weight in consecutive sets. Never.
5) If you are not sure, on weight and reps, add weight, reduce reps
6) Perfect form is NOT a necessity for all reps (dont injure yourself but cheaters reps with heavy weights are VERY effective)
The last principal is one that I use because of the psychological impact it has, and it may not be for everyone:
7) I train my bis and tris together, alternating sets, in a workout of just arms. I do this because the rush of fully pumped bis and tris simultaneously, gives me, momentarily, the biggest arms I can have and it motivates me better than working one or the other on separate days and as secondary workouts.
Follow these basic principals for any arm exercises for a month, eat right (plenty of protein) and get your rest and I guarantee you that in the first month your arms will grow more than they have been.