When faced with odds that are stacked against you (For instance you're alone and you have 1-8 undead bearing down on you and you cannot run) there are things you can o that drammaticcly increase your chance of survival
1) DONT PANIC. Panic is what gets you killed. If you panic you wont think clearly, you might run yourself into a corner, hurt yourself somehow, or a variety of other things that could kill you. Try to stay calm
2) If you have a gun, use it, but only do so as ammunition effectivley as possible. If you can help it, dont aim for the head or the center mass. The head is a small target, you might not hit it, and each wasted shot brings that zombie one step closer to eating you. Shooting the center mass will likely slow it down for a second, but then it keeps coming. You waste ammo shooting it in the center mass. If you can do it, shoot out the legs, they cant go very fast without them. Once you've immobilized them, deal with the situation as you see fit.
3)If you are armed with a melee weapon such as a knife, crowbar, etc. Try to use its weight to your own advantadge. Momentem has effect if you let it build it up, alot more force in your swing means alot more damage if you're using that kind of weapon. With a knife, Try for the neck. Both the corotid and juggular arteries are there, and since undead still have bloodflow to and from their heads, taking out these veins will put them down, garenteed.
4) If you have no weapons at all, only your fists, then attempt to use you're setting to you advantadge. (EX: lead them into a doorway them slam the door in their faces, lead them over sharp drops or step ups so they fall over, etc.)
5) If worst comes to worse, you may have to resort to hand to hand combat. It's reccomended that you wear some sort of armour anytime you're outside and exposed to threats (soccer shin gaurds, elbow gaurds, hand gaurds, etc. will do, since they'll protect well against bites at least once) but If you are caught without your armour, try to pull your clothing over exposed areas of skin (EX: If you're wearing a long sleeved sweater but your hands are exposed, pull them inside the sleeve) This may not provide very much protection, but it might be able to stop a light bite from puncturing your skin.
When engaged in hand to hand combat, you're more than likely going to be outnumbered which means they are stronger than you. Even if they dont outnumber you, they might still be stronger. Dont try to be Rambo and hold your ground in a Melee, but dotn run away either. Make stratigic fallback moves (EX": put one down then back up a few feet, wait for them to come for you). DO NOT CHARGE IN! If you do this, they have the advantadge. Wait for them to come to you, and deliver the first blow. Dont try to directly kill the undead in question, but rather try to knock it over or something akin to that. (EX: Deliver solid punches to the head and chest, kick out the legs, grab the arm and pull it over) Remember that essentially anything that works to put down a human will put down a zombie. There are alot of effective combat moves out there that can put a person down in a matter of seconds. Cup you're hands and slap them quick and hard over their ears, it results in a mild concussion, that will most likely dissorient them and give you a little running away time.
Anything you can do to knovk it over or disable it. If you can, try to kill it while its down, not while its up. Stopm on its head. And thats the end of that.