I couldn't help adding my thoughts on ass kicking...
Fighting is not necessarily a good thing but sometimes it happens. What you really should remember about fighting is: If you think you are going to get into a fight, hit first and very hard. A good straight punch to the face, don't swing your arm like a roundhouse punch or something like that, they'll see it coming. Aim three or four inches behind their face when hitting them. Go hit for the nose or jaw or eyes, you want them to be in a lot of pain. Hopefully, you'll immediately floor them and it will be over with that first punch. If they don't crumple and fall to the floor within a split second, hit them again and again until the fall down.
That is your pretty basic, no-nonsense method of fighting. I'll move onto a few other techniques that are a little more destructive.
1.) Compounding. Compounding a strike is very simple. What you want to accomplish is stopping the sway of your opponent's body when you hit it. This can be done firstly by backing someone into a wall and hitting them or grabbing the back of their head in one hand and elbowing them in the face with your other arm. I recommend the first method for people who don't really fight often, as there is a lot of risk in grappling with you opponent.
2.) Blocking and Trapping. If you can't floor your new friend with one or two hits you're going to want to know how to block. Hopefully, the person you are fighting will throw roundhouse punch or take a big swing at you. Step in closer to them and hit their punching arm with your forearm and hit it hard. It'll hurt you a bit, but it will hurt them a lot more and probably knock them of balance. Punch them in the face. From here you have two options, either punch them again, or, if they leave their arm hanging in the air, hyperextend it and hit them in the elbow. You'll break it, it only takes seven pounds of pressure to break locked elbow. The second option is essentially trapping their limb.
3.) Kicking. Never, ever kick above the mid-thigh. Kicking any higher puts you at high risk. The last thing you want is to be thrown to the ground. You can kick to the groin. A hard kick mid-thigh causes little long term damage and lots of short term pain. This is a good thing. A well placed kick will discourage anyone from continuing. Go for the sides of the knees if in doubt.
4.) Dancing fighters and how to move. Some people move around a lot when they are fighting. You can use this to you advantage, but always remember, they are moving around to "fake you out." Don't look at their face. Look directly at their chest if you are fighting a guy and around the belly button if you are fighting a woman. They won't be able to fake you out. You also could try dancing around, though you should stop immediately if they start watching your center of gravity. They know just as much about fighting as you do so you should end the fight as soon as possible. I generally do not approve of dancing about; it really wastes a ton of energy you could be breaking your friend's face with. Keep your feet about shoulder-width apart, your knees slightly bent, one foot six or so inches in front of the other. If you have to move shuffle, don't pick your feet up off the ground; take your weight off it and slide forward.
5.) Being particularly nasty. Here are a few evil tips. Slap someone in the side of the neck. Your neck has %400 more nerves and sensors than any place else on your body, besides your naughty bits. Put you knee into your opponent's leg halfway between their knee and hip on the outside of the leg. You'll hit a nerve. Poke them in the eyes. Grab their throat between your thumb and index finger. Whether they live or die when you have their throat is up to you. If you squeeze too hard, you'll most likely break their windpipe. They'll die, that's bad.
Going psycho. Don't. If you are really pissed off and aren't thinking you are going to get hurt. Bad. Don't talk trash either. Keep your mouth closed and you jaw clenched. It'll save you chipped and broken teeth and maybe even biting off your tongue.
There's your basic guide to fighting. Let me recount a few essentials. Hit hard and don't hold anything back. Don't kick above the thigh. Don't mince about like a fairy.
Disclaimer. I've studied a good amount of martial arts for a good amount of time. Karate, American Kenpo, Jiu-Jitsu, animal kung fu, and Pak Mei with a little Muay Thai for good measure. I never learned any martial art for the sole purpose of kicking ass and don't think anyone should fight using any of the above techniques unless their life is threatened. Hurting people is bad.