Stop to fire! Firing while on the move makes you harder to hit, but it makes it almost impossible for your gunner to hit anything.
Take special care of your skilled gunners. Give them your best loaders and remember which tanks they're in; these are your aces in the hole.
Once you've spotted an enemy, move into line formation. If you're American, spread the line to maximum width and approach the enemy to try to get in side shots. If you're German, you'll probably want to stand off and let the Americans come to you.
Don't forget your artillery strikes. Smoke is an invaluable asset that will let you get closer to or flank an enemy.