Read up on some basic tactics, even on the worldoftanks.com site is a good start. The videos on penetration and camoflage will help you understand game mechanics pretty well. I got into the SPG line early so that I could hang-back, watch games unfold a bit from artillery-view mode, and see how people hid/moved around the maps. It also helps you when you start playing as a tank/TD to know a bit better where SPGs can/can't hit, etc. And when you get to the Tier 4 tanks, especially if you're still in a light, don't get discouraged. You won't always have such a great disadvantage with the MM. I almost gave up the game at tier 4, since I kept being thrown in with tier 8s. But getting out of a light helps. And, quite honestly, it takes a lot more skill to play a light tank well, especially in those odds, than it takes to play most other tanks, in my opinion.