This is becoming more common it seems. One thing I have learned to always be prepared for is needing APCR ammo to deal damage to a tank that is above my tier. I first noticed problems when encountering t29's or Tigers when I was just starting with my M6. I could take 3-4 shots and no damage was dealt because the armor is too thick. Unless I was able to maneuver around to flank or get behind, I was in trouble. Loading APCR ammo does allow me deal damage from positions that standard AP ammo doesn't. Just something to keep in mind.
I avoided that ammo for a while because it's expensive but now I always keep at least 6-10 shells on board for those matches where my tank is in a match and I'm at the bottom of the food chain. I only load it when needed to try an avoid the expense.
Also, look around and try to travel with a friendly tank that is several tiers higher because that gun will deal damage your tank can't and hopefully you can time your shots to avoid being hit while the enemy concentrates on the higher tier friendly.
These are just two things I've adapted into my play and I know there are others that can be incorporated that more skilled players could elaborate on.