The biggest and the most difficult thing to learn and remember is all the tanks weak points. A lot of times esp. in the higher tier matches you may not penetrate the enemy armor because you are hitting it in its strongest spot or it is sloped armor.
Easy way of figuring that out is to look over a tank targeting mod. It shows the weakspots n stuff, even though it recently became illegal to use on if I remember correctly.
Not terribly sure on that one, but the mod's pictures typically contain the weakspots.
Worst case scenario, since I own most tanks and have fought against every tank I can show ya guys some tricks if ya want in a platoon battle.