I got tier 30 after grinding about 18 hours, so my suggestion will be for average players:
1. win or lost makes no difference, but farming damage/capping gives good points. Any fast win or loss normally will make your rank end up like captain (half points of general)...
2. I use hull down tank as my first tank (like caernavon ax, centrion 5/1), which actually works well. there is a hill on the west starting map, you can simply stay there to shoot your front or down to the cap circle. I once got like 6000 dmg in that position at the early stage of game. T-44-100 or lorr 40t is my regular 2nd tank, for their mobility.
3. use heavies when you are defending around the city (final stage), like IS-3A, VK100.01P, side scraping at the entrance of bridge, it works very well. I got normally 3k-4k dmg before I got killed by air strike/arty.
4. I think the best skill is spotting "or recon", and Arty/air strike are too situational (they works against lightly amored tanks, and dense group of tanks only). I got quite a lot of assisting dmg when spotting bush area.
5. when you failed to defend an area, you don`t have to retreat, if your amor is at least 70mm thick and full HP. that once arty shot will take half(or less) of your HP...that means if you are in a good position, just keep holding it, sometimes enemy are just plain stupid and keep pushing, you can shoot them from behind...
7. Defending also gives you good points/exp, but, it`s just harder than attacking.
8. the reward tanks are just too expensive, in terms of times you have to spend...