I hear this alot not really in the form of a question but a guy at the gym will say damn my arms are lagging or my arms just aren't keeping up. Then its usually I need to hit them harder.
In all reality though the problem doesn't sit with not working them enough its over training them.
Think about all the upper body exercises you do that don't target the arms but your arms are still part of the lift. Im not at all saying stop training your arms but to look at how much and how hard you are using them through the week.
All your muscle groups need to be worked then they need to heal if you don't allow your arms to get the rest they need they will not grow at the rate you want.
Me personally I split my muscle groups to work each group and get the right amount of rest which leads to the right amount of growth. Its a hard balance to figure out but I will say that its definitely a person by person situation.
I reccomend that on your arm day train them just like you would any other group. Just as your training them remember that if you can feel they are being over trained. Take a step back and let them rest. Switch up your arm workouts just like any other group and try to find the mix of 3-4 exercises that you can feel aren't pushing you up to the limit of almost an injury because of over training certain muscles between your shoulders and forearms.
Good luck and good gains brothers