Just to get started I will quickly cover the basic controls and things you can do with your tank.
Yes I know this will be quite trival for alot of you reading this, but I put it here just for the sake of completeness and the odd person who was unaware of a particular control. Feel free to skip.

How to move your tank
Yep you probably guessed WASD will move your tank around (no big surprise I know).

How to rotate the turret
you can rotate the turrent with the mouse. It operates on a tracking system and rotate towards where you are looking and stops when it get there.

How to change seats
The default key to change your seat in the tank or any other vehicle is 'c' most tanks have a variety of seating arrangements from driver/gunner to machine gunner and plain old sitting of the back because your legs are sore (lazy bugger).

How to change view
Some tank positions provide different viewing angles which you can change to and from with the scroll wheel of your mouse. Look out the hatch or from the saftey of the slit box as I call it. Need a zoomed in view? Jump into precision mode.

How to change gun range
Honestly I'm not sure what the default is because I changed it to Q and E. But you can dial the distance of the guns on your tank in precision mode the crosshair will adjust to what you set the guage too. Not sure of all the tanks but most should cater to ranges at 100m increments.
(check in you keybindings for these controls).

How to change ammo type
There is a variety of different tank ammo avaliable some which you will need to buy in the modifications screen of your tank. Your tank ammo loadout will be mapped to the keys 1, 2, 3 ect

HE = High explosive - Useful for killing infantry as it has a decent blast radius ( not very effective against armour)

AP = Armour Piercing - The ammo thats great for killing tanks but not very effective against infantry (unless you like the thought of punching a big hole through their bellys) There is genarally more effective AP rounds avaliable in the upgrades section that is alot better and not all that costly.

MG = Machine gun ammo - Often a machine gun is also mounted to the main gun for quick infantry kills with no reloading time between shells and machine gun ammo (missed your HE round quickly flick to mg if you cant wait to reload the round).

Well that pretty much sums up the basic controls, very unexciting I know.

When fighting tanks of a similar class, it is often the case that whoever lands the first shot will win the fight. If you can catch your opponent unaware and land a few rounds on them before they spot you it is ideal and will often lead to their demise, however if you find yourself hit by an enemy, retreating behind cover "may" be your best option.

The Exit Plan
Too often I see tanks position themselves in a compromising way that if they are caught unaware it pretty much means their demise. When positioning your tank be aware of what is around you, rocks, trees, buildings all have the ability to hinder your escape when under fire, That however is not an excuse to park out in the middle of a field. Make sure when you park your tank you leave the front and rear open last thing you want is to die because you backed into a tree or other obsticle, same goes for the front. Give yourself options to escape, don't limit your options by being careless.

Cover
Another thing you can do is give yourself proximity to a cover object, dirt mound, hanger, whatever as long as it can conceal your tank it may keep you alive. However those pesky AT Infantry may find it easier to sneak up on you so it is always a good idea to find cover that is out of the way of the front lines (where high infantry activity is present). You should choose cover that is relatively open so you can see potential flankers coming before they reach the cover. You should maintain good sightlines in as many directions as possible.

Bombers
Trees are a great escape from the bombers roaming the skies. If you find yourself getting bombed to death by this flying menace, find yourself a nice clump of trees to hide in. You may be able to shoot a couple down athough it is quite challenging. Pilots are also a resentful bunch, if you shoot them down they will make it their mission to destroy you. It may be best just hiding from the planes and moving from tree line to tree line as they pass. Also if you hear a plane overhead stay inside the tank, popping your head out will make you more vunerable to their bombs as well as any infantry lurking around.

Mine Awareness
It is important to scan the ground infront of your tank as you drive along, particulary when crossing through choke points such as bridges, gates, around objectives or any other high traffic areas. Also keep your ears open, alot of pesky infantry will plant mines behind, infront or just next to your tank. And in many cases they will shoot them instead of waiting for you to run over them. The sound of a click or clunk may me your cue to exit the tank and deal with them.

Map Awareness
Knowing where the anti armour caches on the map are is a great thing to know, not only for when you want to take out a tank but for your own survival as well. Keep your distance from these points to insure opposing forces can't land an easy kill on you.

Teamwork
Teamwork is one of the core aspects of this type of game. Regardless of the type of weapons the enemy has access too or your own arsenal. A well coordinated attack can turn the tide of the battle, have infantry and other armour in your vicinity to help you fend off any surprise attacks and do the same for them. A lone soldier or tank crewman cannot insure victory on this type of playing field (without teamwork, without hope). Even a crewman with only a spanner in hand can be a useful asset as I proved in an earlier game I played. I pretty much ran around behind a friendly tank repairing him as he was taking fire, he was quite pleased with my effort and thanked me for the support.

Angled Armour
As you may have noticed loose projectile shots will sometimes result in the shell being deflected.
It is a useful tactic to position yourself in such a way as to increase your chances of deflecting shots. If the front of your tank is 12 o clock, try positioning your enemy at a 1:30 or 10:30 position, this requires experimentation with the different types of tanks as the angles vary. I also find having a slight downward slope can help assist this. Also remember your tanks corner or centre point will have the tightest angles so if you can hide this vunerable area that will help out also.

The Spanner
A spanner is really a must in my opinion for a tanker who values his equipment and quite frankly nothing is worse than driving around with a big black smoke trail. It is bad for the environment, but you also have a big black flag over your head just begging for someone to come kill you, not to mention the fear of the imminent one shot death you will be rewarded with.

So you have a tank in your vision, he hasn't seen you yet infact he's not even looking in your direction (lucky you). You could fire now but have you scouted the area? Perhaps you get a quick kill and ride off into the sunset but perhaps you don't. Remember tanks will often travel in packs, before you blow your cover and send a signal to all the tanks in the area that there is fresh meat waiting to be killed, do a quick scout of the area for potential hostiles that are more threatening then the oblivious hunk of metal staring the other way.

So you did your scout and thank god you did as you spotted another two tanks in the area none of which have seen you. Firstly you should pick your target, I'd go for the one that poses the biggest threat to "my" hunk of metal. Conceal yourself from the other two tanks, you will blow up really quick when getting pummeled by multiple tanks so play smart and take that option away before you engage. Once you take out the first one isolate the next one ect, 1v1 tank battles are far easier to win. Make sure you repair any damage you may have received before moving onto the next target.

It is preferable to hit the tanks in the rear armour as that is the weakest, if not go for the side armour be careful not to get caught out if you decide to flank the enemy. You should also try to hit the tank at 90 degree angles, if your angle is too loose it may just bouce off (especially with heavily armoured tanks).

Although it seems difficult in theory to turn a tank invisble, it is quite possible to not even let your opponent see you and if they can't see you then they can't possibly shoot you right? (well in most cases anyway)

Camo
An easy way to gain the upperhand is to fight in the shadows, nothing sticks out quite as much as a black blob sitting in a wheat field, why be that guy who thinks he's invincible because hes surrounded by metal plates. Your better off being underneath a tree where the tanks blend really well into the environment, that few extra seconds it take for them to find you may win the battle. This is not the only option avaliable but is by far the easiest, you could instead opt for hiding behind low hanging tree branches this does however limit you own visability, the use off spotters and angles can however help you with this, particulary if you happen to have a nice mate in your tank ready to do the eye work.

BlindSpots
Using blind spots to your advantage can turn you from that hunk of metal into a real war machine.
It can take some quick manuvering and a chase route to secure the kill but is very rewarding and quite fun once you can master it. Basically you use enemy cover to your advantage, as the closer the object is to the enemy the greater the blind spot. Position yourself between the enemy turret and a cover object that is closer to them for example a tree or crate they will have a hard time hiding behind the tree especially if they are side on to you, but you on the other hand are sitting in a very large blind spot they will need to move to even get a shot on you if they can even find you that is.
when they start to move try to mirror their movement and keep his turret behind the object. WOOO its like taking candy from a baby. (disclosure: taking candy from a baby is just plain not nice and may result in a slap in the face and I do not condone such behavior).

Although height is a great advantage to have there are some pitfalls. Firstly as a turret can only point so far downward you can be vunerable from the base of whatever hill you are on, you may find it preferable to aim your tank slightly downhill so you have coverage on this area. Secondly the terrain of hills are generally quite rocky, bumpy and have alot of trees which hinder your mobility. Trees and branches also have a tendancy to block quite abit of you visability so there is that to consider aswell. One other thing to note is you put yourself at a disadvantage when it comes to AT infantry, they can flank you quite easily and with your mobility hindered you almost stand no chance.

Using High explosive shell on infantry at a distance can be quite tricky when shooting across dead flat ground, because the distance and shell drop can be hard to judge on this sort of surface. Gaining a height advantage in this situation will help tremendously, especially when there are constant lines of infantry reinforcing an objective point. you really dont need much height to make this effective.

I personally find small hills or just plain old elevated ground to be the most effective positions to take because they give the most advantage with the least pitfalls. Small hills that you can reverse down the opposite side enough to cover your tank if you start taking fire are a good alternative to being up the top of a mountain.

Using the hatch to view your surroundings is sometimes a risky buisness knowing what precautions to take and when to use the hatch is a debated topic, I hear some people say never pop your head out the hatch and I agree to some point. That being said there are times when it is better to get a view then to risk getting flanked.

Firstly you should always limit the time you use the hatch to only getting a quick 360 of your surroundings. Always keep you head inside when in high traffic areas such as capture zones especially ones that are on the front lines, when moving between and around buildings (whenever possible avoid these areas altogether), when bombers are flying overhead, when taking fire and when there is known infantry lurking around.

When you are away from the frontlines and not in any direct line of enemy reinforcement is is generally ok to get a "quick peep" and I do mean just a quick peep to check for jeeps and the like that are heading your way. The fact is that if you're away from the battle zones chances are that only AT infantry are going to be in your immediate area as people who can't combat tanks will try to avoid them (at least the smart ones), as a soldier I wouldn't treck half a mile to sit next to a tank without anything to destroy it. Snipers will occasionally look your way but if you keep peeping to a minimum they will generally get bored and focus on the lines of infantry pouring in and out of objectives. In truth I have saved myself more times than I have been shot out of the tank using these simple guidelines.

Once you have become accustomed to your tank and all its controls you should start getting used to shooting on the move. Shooting while driving can be more difficult and whether you should do it depends on a few things, mainly what sort of enemies you are facing and the terrain you are driving on, maps like the airfield are perfect for this sort of strategy.

When plenty or even a few skilled bombers are flying you may be better off sticking to the few bunches of trees avaliable or heading out on the outskirts. If you are getting obliterated by them try jumping into an infantry role and using the flak cannons to chop a few down or hide in the trees and shoot them down with your turrent and mg.

When enemy tanks are roaming around be careful about driving out in the open and its best to make sure all flank routes are closed off so you dont have tanks suddenly spawing behind you. Keep the enemy reinforcement lines ahead of you and try and circle around their side and rear flanks when engaging. Its best to stay within you own territory and not get caught out behind enemy lines.

When engaging tanks stick to the flat ground while moving, one small bump will send your shell flying up into the air. Keep your turret in the front half of the tank and preferably the front 45 degrees. There are times when you need to have your turret backfacing such as a persistant jeep with AT soldiers trying to come up your rear or even AT soldiers on foot trying to place a mine on you, if this is the case you need to keep moving and lead them into friendly troops if you're having trouble landing your HE shells or machine gunning them down.

The advantage of staying on the move is great, particulary when the enemies main source of anti tank weapons are soldiers or light tanks, you can pretty much negate any attempt to mine your vehicle and rockets or panzerfausts are considerably harder to hit, especially at any sort of range. That and already being at top speed enables you to get away quickly if you took abit of damage.

Beware of the sneaky guys wanting to mine your vehicle. I once had a game where we pretty much obliterated the entire enemy armour force and were about to win the game, I hadn't lost a tank all game but had shot down about 6 or 7 and a dozen infantry including a jeep trying to tail me till I stopped ( which I didnt hehe ). Being a good team player I stopped when I heard a guy whistling behind me figuring he wanted to share the tank, but no it was a sneaky enemy planting a mine on me :P (I had to give him props for that).