Don't forget the following beauties, although I might've gone off topic a bit.
Pick up a hitchhiker to sit in the machine gunner's spot on your tank and mindlessly chew through round after round all over the place, giving the enemy roughly 10 minutes to prepare for your arrival.
Repeatedly shoot the main gun vaguely in the direction of where some enemy troops might just happen to be.
Get out of your tank to repair without first checking your immediate surroundings, forgetting of course that empty vehicles show up on minimaps.
Get out of your tank and jump on top of it to use your binoculars.
Don't use the third person camera views to make sure the main gun on your Panther isn't sticking out of the barn/shrubbery.
Don't switch to the 3rd spot on the StuG when you're trying to be all stealthy. Yeah, being able to see 360 degrees around your vehicle without making a sound is a surprisingly well-kept secret in this community.
If you're in a fast tank such as a Cromwell or Crusader, make sure to completely ignore your overwhelming speed advantage and be sure to stop and fire at the Tiger head on.
Don't take the time to learn how the tank sights actually work.
Be sure to ignore what the vehicle you're driving was actually intended for. Go take on those dang Panzers head on in your M10, go throw your Jagdpanzer IV into that crowd of T-34s.
Ignore the fact that turning your main gun (and, to enemy infantry, your field of view) away from where they are, only to switch to the hull MG and cut them in half is a good way to deal with infantry.
Make sure never to bail Shermans or Panzer IIIs, but feel free to bail the odd Firefly and King Tiger whenever a pesky anti-tank gun scratches the paint.
If you hear that clank of a satchel charge being thrown on to your tank, drive off at full speed. Don't worry, the satchels NEVER fall off, no matter how fast you're going.
Be sure to drive into that flag next to all the houses with tons of windows without any infantry escort to cap that flag. After all, how will you be 1st at the end of the round if you haven't gotten those 2 points?
Don't do any single player practice to find the weak spots of enemy tanks, just fire at them as soon as you see them and everything will always work out in your favor.