Don't be in a rush to "tier up". Play a Tier II until you feel competent, and have some measure of situational awareness.
Get some stat-tracking. Use something like wotlabs.net. Watch stuff like your WN8 over time.
Dish out more damage than your tank's hitpoints each game... consistently.
Learn to watch the map constantly. Avoid target tunnel vision. Map, map, map. It's like Dora the Explorer. It's all about the damn map.
Know when to go back to base to defend. Know when to push on to the enemy base and cap (and when not to try to cap).
You do this by not throwing away your own hitpoints on "bad hitpoints trades".
Never, ever suicide just for the hell of it. Every game is an opportunity to deal good damage, learn something, pull out of a win from thin air... or watch someone else do it and learn from that, too.
Record your battles and watch them again later, to review your decisions.
Learn when to use premium rounds (not in Tier 2 - later

), when to use HE (rarely, but there ARE important times), and how to use AP effectively.
Learn weak points in all the tanks you face. Learn the STRONG points and the bad angles you should avoid shooting at.
Learn the spotting mechanics. Why enemies sometimes shoot you without you even seeing them. How you can do the same.
Research the right crew skills. Learn how to build up crew skills efficiently.
Play a number of tanks, in different roles, every day. You get the 2 x bonus on more vehicles/crew that way, and you learn the roles those tanks play. And their foibles (eg. gun depression problems), weak spots, etc.
Learn to spot when you are on "tilt"... ie. when you're playing like crap, but continuing on playing back-to-back crap games like a gambler looking to "win it all back". Stahp. Go do something else. Come back later with a fresh head.
Hope that helps!