How to get bigger arms, Step 1 have the right genetics. Step 2 congrats you now have big arms! I wish it was that easy, and for some lucky individuals it is... but not me and perhaps not you. The easiest way to get big arms is understand the fact that they are not loaded with androgen receptors like your shoulders. For a lot of people they just take time and patience, however from my experiences training I have learned what has helped me develop my arms.
I guess I should also mention I don't have huge sleeve busting arms, but they are a LOT better then when I started the gym, and the people who work hard to get something typically have more information for you then someone who was just given something. It's pretty easy to pick out someone with great calves or arms and ask what they do for them. Likely they will name off a couple of their favorite exercises and go on how they have great genetics. These are not the people you should listen to, it should instead be the people who you know worked their ass off to achieve something. I hear often how Marcus Ruhl has poor triceps or Dennis Wolf needs more calves and hamstrings, while everyone would be rushing to Lee Priest for tricep advice or Branch Warren for hamstring info. You should be paying attention to the underdogs, the people who have worked incredibly hard for what they have even though it may be not much, because let's face it, to say Marcus Ruhl or Dennis Wolf don't give it 110% at everything they do would be just not fair. Anyways enough rambling and here's what has worked for me.
On arms train volume period. I myself don't personally care if Marco can curl 65s,75s, or 155s...ok 155's would be kinda cool, but I hear again and again that a bodybuilder could do a heck of lot more with 20s then some new gym rat with 50s. I like to train in rep ranges above 12 up to 20 reps on some movements.
For the longest time I unknowingly struggled with this one. I did pushdown after pushdown thinking I was achieving something, when in reality I was likely achieving a nice case of tendonitius in my elbows. Keeping your elbows static throughout the movement seems to be a common theme among training arms, also not flaring them when the weight gets heavy and if you are flaring them, decrease the weight. If your ever in doubt of your form or whether your achieving the best contraction just try closing your eyes. You'll be amazed at the sense of muscle mind awareness and how your body will make the small corrections needed to isolate whatever group your looking work.
I believe sticking to the basics for arm training. That's barbell curls and tricep pushdowns. I don't think movements like isolation curls and alike have any place in someones repertoire, if not anyone's.
4. Don't train all angles
A lot of people tell me to train from three angles for my triceps to hit every head. This may be true for advanced bodybuilders who need just a little on their left medial tricep head, but I think for the average gym goer 1-2 movements with an adequate amount of sets is PLENTY for optimal contractions. You don't want to overdo it and chances are you are with 3 different exercises with 4 sets a piece.
5. Do your compound movements
I train primarily powerlifting now and I definitely see a difference in my overall size from my moderate arms to my puny calves. I do believe the big compound movements (Bench,Deadlift,squats,OHP) contribute to overall bulk and will help development of all muscle groups.
This is entirely preference. Currently I train triceps after chest and biceps after shoulder, both once a week. My best results were training tris with chest and bis with back and then having a day where I would train something random with arms.
I could go on and on ,but for today I'll settle at supersets. I have a love hate with supersets. My best pumps have always been when I supersetted my biceps and triceps, but I think this may have always just been pump because outside the gym my arms always seemed to deflate to their normal size.
This is my take on it and I'm sure in a year I'll have another take on it. You take your take on my take and figure out what works for you :)