The beauty of arty is,
Its random, as it should be. there is only so much to do when it comes in, and you don't know when it will come in
BUT
We are blessed to have feedback for mortar and howitzer, so you can hear it for a sec before it comes.
ALSO,
there are 2 ways to deal with it,
Hide, Avoid or move like you have a purpose
OR
Kill the spotter.
MOST
arty gunners or mortar men don't fire blind unless they are at point blank range. So you can almost always stop arty when you realize its zeroed in on an area. Simply Kill that spotter.
BONUS
You might also be taking out a squad spawn in doing so, since I think, more spotters are SL than scouts.
And a good percentage of non-SL sppotters are snipers - Also a great threat to nutralize.