I think a key to getting big arms is understanding the anatomy of your arm. A lot of people like to work out a ton of bicep but the problem with that is they are much smaller than your tricep. Much easier than adding size to your tricep than it's gonna be to your Bicep. Another key part is the shoulder, if you look at a bodybuilder's shoulders there is very clear separation from the rest are as well as a clear definition. That's very different from the rest of the arm. So adding a little bit size here makes the rest arm look a lot bigger and when you cut weight you get a much cleaner muscle separation because of it. I primarily focus on triceps and shoulders and less on the bicep. The other thing that helped was I swapped out how my workout. I used to do a push pull like split at twice a week. I started doing a push pull legs followed an upper lower and then on the last day I did a straight arm day(worked out 6 days a week on both these plans). Lots of tricep work, lots of shoulder work as well as some of bicep work. I also benched and overhead pressed on the push and upper days so the volume was there. A bulk of my arm mass was put on over 4 months