well, theres no immediate guidlines, but ill try:

mortars are pretty much useless until you can get them to a decent experience level (3-4), so keep them firing in your armies, in conjunction with some other arty.

howitzers are typically very accurate, but i don't think they can get quicklime. not sure, but i think.

foot artillery are usually straight-firing, so you may want to keep them on hills. if you have them on a higher hill, then canister is much more effective; it doest hit your own men.

horse artillery is usually accurate, but against forts its crap, and the shots hardly hit more than a couple enemy.

canister shot is best used only when the cannons are uphill.

quicklime/other quicklime-like shot is best used when the unit is standing still. otherwise, it will almost always miss.

explosive/percussion cap shells are best used against enemy artillery first, and then marching troops. they are good all-round, but they are the only effective shot that gets marching troops in my experience.

shrapnel shot is my bestest friend when you get it! just think: the accuracy and range of roundshot, but that explodes and rains shrapnel down on the enemy! oh, sweet, sweet shrapnel shot........