All the arty I play with 3 exceptions are all about quantity not quality.
The more shots the better, I hate a full tube. So I usually have a camping spot picked out, either a well known one or a place I saw trees go down.
After every shot, I press the S key, usually before the shot has landed. As I am doing so, I choose where to move to get the best line of fire on my next target.
I choose on, who makes the most requests, from my unique view, who I feel needs the support,, or where my personal risk is the highest.
I move for the obvious, counter battery, but it kills the load time, allows time to look at maps, and then still allows you to park, pick a target, aim fully, fire and reassess again.
I always try and choose those already or are about to be in direct battle with teammates. My damage will have immediate effect as well as collecting assist points.
I try to keep that in mind as assisted damage is artillery bread and butter. The more support you provide versus your own HP collection or kills makes the XP difference.
The more stun or critical hits you get, the more potential for assist points, and more XP.
I only play tier 5 and above, so can't speak for the smaller guns. I aim to miss. Instead of missing over a victims head, I will purposely aim short, so a ,miss will at least splash tracks and stun. Groups of enemies, I aim to miss between them, to splash as many as possible.
My exceptions. The fantastic Bishop , FV304 and Crusader SP. I have a riot with these 3. They all have low damage potential. The short range adds to the fun by providing another challenge, keeping safe.
To make up for that, the accuracy and load times are great.
Like throwing anything, the closer you are, the better the shot. I can choose where on the target to aim for. Back deck for engine or fuel. Front to kill driver or wreck gun, and the simplest, tracks. I can easily shoot through windows, or through holes in the roof on Pilsen. With that fast load, it is easy to pick a red in trouble or daft enough to get caught in the open. Track him, and keep him stationary as the team feasts and I collect the assist points. Great XP.
What the magic formula is, not sure , but the equipment I bought, 4-5 skill crews can only have helped. I spend more time looking for assisting than killing or collecting HP .
dfw above, mentions the battle assistant.
The vanilla client has a version. They incorporated it from the MOD a while back. There were a few small differences, I have not tried the mod since, but it will work the same anyway. A different view, that gives you an approximation of your shells flight path.