Multiple attackers. Sounds pretty scary, and most of the time it is. Just when you think you've got the situation under control, another little zombie comes along and bites you in the ass. Let's look at some options.
Suppose you're in the middle of a parking lot and six of them are coming at you from all sides. What do you do?
Best course of action in this situation is to look for the biggest hole in their line and make a break for it. What? No fighting? Exactly. First rule in a zombie fight is to survive. Don't be stupid and think you're invincible.
What about two attackers and you have no room to run? Better question. In that case, use their clumsiness against them. Move yourself so the zombies are lined up single file, then push them back. They'll likely fall and you can kill as they get up. Don't get grabbed and fall with them. Then you're screwed.
What do you do against several zombies and there's no place to run? If you're dumb enough to get into a situation like that, the best thing you can do is run to the nearest one and kill it as quickly as possible. Use the body to knock down a couple of others and kill the next nearest. Throw that one to knock down some more and you've created some breathing room.
Always keep moving, don't let them get fixed on you. Get them to the ground and keep your feet. You'll live longer.