I think the most key thing you can do is keep communicating with your team. I was playing City on Nod with about 5 other people and we weren't getting anywhere. One guy said that if we would let the GDI harvester live he would sneak in behind the harvester and blow the GDI powerplant. Problem was, several of our team members would blow up the harvester anyway, and not pay attention to him. So another guy started repeating what the first guy planned, then I started, until finally we convinced everyone to go along with the orders. So they backed off the harvester, he snuck in, and down goes the power plant. Just have to keep talking to your team, I always report any armor movements I see, its a lot easier to prepare for a flame rush if someone reports them when they first exit the enemy base.