It may be too late, but I'll throw it out anyway cause I don't want to see you getting hurt.
Firstly, I'd also recommend not fighting unless it's a life or death situation. We have systems of law for a reason, and that reason is to protect the most precious of commodities, human life. Having said that....
I've been training in muay thai since I was about 7. If you're fighting someone with no experience, you need to assess what kind of a pain tolerance your looking at. If he's a jacked up junkie...wait for him to start it, and end it.
Some basic tips..keep your guard up. Your hands do not leave the spot in front of your chin. This means one hand is always there unless you have such an overwhelming advantage that your opponent has no chance whatsoever of retaliating. Don't flail about, strike with surgical precision. Notice an opening, attack it. Attack it with everything you've got. There's no half-assing in a fight. Most inexperienced fighters will not be prepared for a simple combo, so try practicing for a couple hours by shadow boxing. Jab-cross-hook-uppercut for example is an excellent mix of speed, power, and a variety of angles of attack. You want to run with the uppercut when your opponent blocks the jab, slips the cross, and ducks the hook. If you manage to catch your opponent on the jaw, you will likely knock him out and end the fight. Just hope he's not the kind of fighter who dies on his feet. We can be absolute monsters in bouts.
Now, if the guy's a hopped up mutant....
There are a few hits that'll take just about any big tough man down. A kick, knee or punch to the groin hurts. Don't count on it stopping the guy though. If you hit me in the groin I wouldn't even slow down on my way to tear you apart. People have different pain tolerances.
Contrary to popular belief, it's very difficult to kill someone with a blow to the throat. As in your chances of winning the lottery are higher. Much higher. A hit to the throat will stun. Use whatever's available.
One of the best ways to win a fight is to start it with a simple foot stomp. By simple I mean the way you'd stomp on something if you knew not delivering every ounce of your body into crushing it with your heel would result in your being slowly eaten alive by slugs that secret a powerful acid that digests and paralyzes you while causing excruciating pain. If you do that to the
top of someone's foot, they aren't going to be walking or running after you. I've experienced that particular brand of pain. [Edit: I thought about this and realized I forgot to say: DO NOT do this in anything but a serious self defense situation. An act like this in a harmless schoolyard fight will get you in some serious trouble. Not to mention the fact that it's morally reprehensible.]
Head butts..I know it doesn't sound like a super smart idea, but the top of your skull is thick and makes an excellent weapon. Aim for the nose. You'll likely break it and quite possibly knock your opponent out entirely.
I'm not going to tell you about elbows or knees for self-defense, as most techniques are disfiguring and/or lethal. The above should be more than enough to give you a strong tactical advantage over your opponent. However, keep in mind that if you haven't been in very many (if any) real fights in your life most of this will be somewhat irrelevant. It'll simply be a matter of natural ability.
