This guide is meant for really new players to World of Tanks and are supposed to help them play better on their first few games. These are mostly general knowledge once you've gotten used to the game. Some of these will also help you work better with your team.
1. Don't be trigger happy
It always pisses me off when some idiot got trigger happy and starts shooting like a madman when the match starts. First, you might hit your team mate and that's always a bad thing. Second, you waste ammo and those ammo doesn't come cheap on higher tier tanks. Look at the map and your team composition at the start of the match, look where the others are going and decide where you will go instead of shooting at the nearby ground like an idiot.
2. Don't go into open fields
If you do, don't be surprised if you're destroyed a few seconds later. This should be really easy to understand. Don't go to open field, that's it. Always stay behind cover, especially when there are artillery on the enemy side.
3. Look at where you're going
Yes, you should be focused and go to a good position but do watch your surroundings, especially when you're using a faster tank. Ramming yourself to an ally tank is a good way to piss off your ally and damage your own tank in the process.
4. Do not take cover behind other tank if it means blocking their exit
If a tank is popping out of a corner to shoot at the enemy team, please don't move up behind them and block their way back. If you need cover, move further back or just relocate yourself to flank the enemy. Don't stack up in one place and get killed one by one like lemmings.
5. Divide carefully
If you see the whole team is going to the right or the left, try bringing some tank and yourself to the other side. owning half the enemy team just to have the other half of the enemy team suddenly capture your base and destroy all your artillery is bad.
6. Hide yourself
Those bushes and fallen trees aren't there just for show. utilize them to hide your tank. Do remember though that the effect will vary depending on your tank. Medium tanks and tank Destroyers that act as snipers should stay well hidden.
7. Always try to flank
Shooting at the front side of the enemy tanks are usually a bad idea. Always try to flank enemy tanks. Let the heavy tanks hold their attention, medium tanks should get to the enemy flank and shoot their fluffier side and rear armor.
8. Have HE rounds ready and pick your fights wisely
If you find your normal shells ineffective against certain enemy tanks, try changing your ammo to HE you might be able to damage some modules that way. If changing ammo is still useless, run away and try to get backup from your team mates.
9. Learn the weak spots
You might think learning weak spots are useless and most battle are finished before you get too close but that'd just mean that you never got in a heavy tank brawl. In these situation, the ones who knows the weak spots of their enemy will win the fight. Heck I've destroyed a KV-1 with my Pz 38(t) because I shoot at his weak point. Here is one site to learn about the weak spots of specific tanks.
10. Learn what your tank can do
Open the World of tanks wiki and learn about the tanks you are using or are planning on using. If you expect the KV-1S to play exactly like the KV-1 or that M3 Lee to play like a medium tank, you're going to have a bad time with it. Check out the wiki to learn what your tank can do.
11. Don't use auto-aim
Unless you're using a rapid firing gun with a light tank. Otherwise, you should be using sniper mode(press shift) and shoot at the enemy carefully. Shooting blindly will not kill your enemies, time your shots carefully and focus.
12. Request fire from your allies
You might think PUGs are filled with idiots and morons but they're players just like you. If you need help against an enemy and you have allies near you or an artillery on the base, press T while you aim at the enemy and it will tell your allies to target that enemy. They might not always respond to that, but it wouldn't hurt to try.
I think that's it for now. I'll add more when I think of more stuff to add. As usual, if you have some input, go put it in the comment section.