Tips to playing arty (from somebody who played it day in and day out in clanwars before being burnt out).
1) Know where the enemy will pop up for your first shot. This is CRUCIAL. Like pre-aiming hill on mines. Or aiming at the crest of the ramp off the spawns in cliff. Tanks *will* be there, and if you have any decent player on your team the enemy will be lit.
2) Know where your next shot will be and you better be aimed there when you reload. You have 40 seconds between shots, you better figure out where you need to support during the down time and aim in accordingly.
3) Know when to take a blind shot and when to wait for a tank to pop up for confirmation. You see a static tank go dark, you think he hasn't moved. Take the damn shot. You see a tank wiggle around, and make itself be a hard target go dark... don't bother.
4) Know when to ignore your impending death to deal one last damaging hit to something important. The scout in the backfield will most likely die to something else. You need to shoot that heavily armored tank and get rid of it for the benefit of the team over your life.
5) Know the tanks that have weak top armor... almost every french. The T95 and below american TDs, all open top german tds, etc. These are tanks worth your time to hit. The E3, the Maus, the rolling blocks of steel... perhaps let the tanks engage them while you nuke the weak armored snipers.
6) DO NOT WASTE YOUR TIME COUNTERING ARTY. Move after you shoot a bit and you will rarely get countered. Let the enemy waste their time trying to hit you while you are directly supporting your team.
7) Aim just past the tank that you are trying to hit. If possible put your reticle on the ground one pixel past the target (assuming stationary). This should, if RNG is kind, put the shell through the enemy tank at a diagonal angle and give you some wiggle room if the shell goes a bit long or short. If you place the shell directly on the tank (especially turret), if the shell goes long it will miss WAY long.
8) Know how slope effects your shot. In #7 that is assuming a flat surface. On a downslope the shell attack angle is different. On an upslope it is different (and should be easier to hit).
9) if you have a high trajectory arty (304, conq, NOT THE 261!), you probably want to aim directly on the tank.
10) wait till the circle gets small, play whack a mole, realize how boring it is and how frustrating it is to face, and play a freaking tank. Wargaming has no idea how to fix the game since they introduced arty. They opened pandora's box and now what? I hope for some make believe tunnel map so arty is completely useless. Nothing is more annoying than sidescraping your way to victory just to be clicked on by some hidden shitter that is at no risk 90% of the time.