I must admit that i haven't found artillery to be so lethal as the manual/tutorial warns, but it could well be down to how and in what quantity I've been using them too.

Not all arty has the same uses or fires along the same trajectory, and some of their researchable ammo will also affect both trajectory and range differently. Bear in mind what can do what and how you will use them. e.g. howitzers, rockets and mortars have no reason to be deployed in or in front of your line -their arcing trajectory of fire means they can sit snuggly behind your infantry, without sacrificing effectiveness.

Ultimately, you want to create "killing zones" where your units can blast, shoot and kill the enemy, from multiple directions -ideally catching them in a cross-fire of different ordinance.

Positioning of formations should depend heavily on the terrain of the battlefield. High ground is the perfect place to locate you cannon batteries. Deploying your line accross the hill in front of them will mean that the cannon can shoot over the heads of the infantry and draw the enemy onto your line in their efforts to check the cannons.

It's a shame so much micro is required to use cannister shot, but I would suggest using lines of infantry in a V, opening towards the enemy, with cannons at the point. This means that not only are the inf closer targets for the enemy, they will also be in position to flank fire & charge the enemy -should they choose to advance up the V towards the cannons. This should allow for use of cannister shot on the advancing or engaged (by your inf) enemy, and solid shot for longer range firing.

I haven't teched up enough to use puckle guns yet, but as they have a flat firing trajectory I'm guessing they should be used like close range cannon.