Artillery usage

I need some hints and tips for using artillery. I usually have a card of mortar and tube artillery in my deck but in game I often forget about it. If I have spare points I buy stuff like tanks or infantry. And if I actually buy arty, mostly when I get annoyed by enemy arty hammering my positions, I just send them somewhere and then forget they exist. But no more. I have now vowed to better integrate the most destructive of all weapons in my games and could use some pointers. How many cards do you usually buy and what type? Is non SPG tube arty even worth investing in? Does rocket arty have a place in your deck? And when are mortars better than arty? Is using counter battery worth it or is it just a waste of ressources? Thanks.