Economy knowledge makes the game easier and more enjoyable. If you play wot for more than a dozen hours, you will probably play the game for some time.
First you should decide on 2-3 paths that lead to tier 10 tanks that you have chosen. Save credits while waiting for discounts. You will be knocking stars every day (double experience for first battle won). Buy mostly tanks with discounts. Plan, what tanks will you buy in next 2-3 months so that you can buy equipment for them earlier when it is discounted. Use consumables bought with 50% price drop.
If you're not buying gold, you can get a small amount of it: rarely in missions, but it can be gained in offers of companies like Alienware and Razor, where sometimes all you must do is register to get 300 gold. More information about it can be found on worldoftanks.eu discussion board, youtube.com/user/hallack05 and other discussion boards and youtube channels. Free gold is sometimes added to products related to video games.
If you don't have much gold, first you spend it on training the crew when transferring them to other tank and for resetting crew abilities, of course only during the 50% discount. It is a waste to lose large amounts of experience by resetting with loss, for credits.
It is recommended to benefit from the 3 days premium for 250/350 gold when there are interesting missions/bonuses. Like when you have KV-1 or STUG 3 G in your garage and there are bonuses +50% credits for playing with tier 5 and triple experience for the crew. If you have gold and lots of free time, in one weekend you can earn few millions of credits and train your crew nice.
It is not recommended to spend gold on golden bullets or consumables.
When planning you mustn't forget about garage slots. It is sad when a tank you're interested in is discounted, you have enough credits but you can't buy it because you don't have any free slots. In such situation, you should sell a tier 5 tank, necessarily with stock modules (basic modules like gun or engine, available immediately after buying the vehicle), so that you wouldn't need to buy them again in the future with a loss. With the tank there won't be such troubles since you can use the 50% discount for buying it again. You send trained crew from the tank sold to the barracks.
Few times a year developer gives some "special" tanks for free or allows you to get them by completing short and easy missions. Most frequently those are tier 1-3 machines, rarer tier 4, that cannot be bought. Usually they aren't too good for playing, but thanks to such gifts after selling them you get a free garage slot and some credits.
- gold - currency in the game. Bought for real money.
- premium account - bought for gold for a limited time. Gives +50% more credits and experience for each game.
- gold ammo - ammunition that is many times more expensive that the standard one, that gives you greater penetration (and sometimes greater damage or larger damage radius in case of artillery).
- tier - tank level
- premium tank - a vehicle that can be bought only for gold or real money, sometimes gained in special missions or 3-4 times a year given away by developer (only weak low level tanks). He earns 50% more credits. Allows you to transfer crew without losing experience as long as it's the same tank class and nation. Usually plays only against tanks that have no more than 1 tier of difference.
- garage slot - place needed for new tanks. Available only for gold.