To make your arms get bigger, you must know how to train them effectively. Arms, like other muscles, should always be worked thoroughly, but in cycles, to let them get bigger. There is no group association to privilege, work your arms when you want.
Arms, like all other muscles should not be worked at maximum intensity all year.
Also note that if you use a mini-cycle, you can avoid this principle. The idea of a mini-cycle is to have for example a week with a heavy training and another with a lighter one. (Source: all-musculation)