It happens.  Drunk people shove.  Kids pick on other kids.  Ne'er-do-wells never do well.  Eventually, most people find themselves in a situation where violence is inevitable.  But, who will play the victim in the scene?

Well, that depends on who is the most prepared for the situation.  You don't have to be a kung fu master, boxing legend, or MMA champion to win.  To win in most scenarios, you need to know a few basic things.

1. Avoid conflict.  Don't be a bad ass.  You cannot tell from looking at a person how well prepared they are to fight you.  You can't always tell whether or not they are armed.  You can never know how desperate they are to win.  Don't be brave.  Don't go down swinging.  Don't puff up and stare off.  Don't fight or bluster unless you have no choice.  Say you're sorry even if you aren't.  Walk away even if you don't want to.  Stay calm and even-toned.  Maintain eye contact without making it a staring contest.  Always watch the aggressor's hands.  If they move to their chest or face and you are within arm's reach, step back.  If you lose track of a hand and you are within arm's reach, step back.  Talk them down.  If all this fails, know that what you do next is a matter of survival.
2. Keep your distance.  Unless you are taking a swing, stay more than arm's length away from the aggressor.  You may not be faster than your opponent, but distance gives you extra reaction time.  Use it.  In a fight, distance is everything.
3. Make noise.  You want to draw attention to the situation.  You are in a fight and shouldn't be.  Make sure everyone knows it.  Make eye contact with someone nearby and tell them to call the police in an assertive voice.  You want this to end before you are hurt.  Getting others involved can sometimes do that.
4. Keep your hands up.  Guard your face, throat, and chest.  Keep your elbows down at your side, though, to protect your organs and ribs.
5. Know that you will take a hit.  It'll hurt.  It sucks.  You will not end a fight without taking at least one hit.  Know that most punches are wild swings and are going to leave a mark.  Get over it.  If you let the fear of being hit paralyze you, you will lose.  Just accept it and move on with the business of winning.
6. Go for the eyes and throat.  In no holds barred MMA matches, there are few rules.  Among the rules universally accepting by most every fighting sport are "don't gouge the eyes" and "Don't jab the throat."  There are serious fighters with serious skill.  Ask yourself why they all agree not to do this with each other.  Answer: because it ends fights...quickly and badly.  Doing this is serious business.  I am not telling anyone to blind or kill a person, but I am saying that these two techniques, easily performed by people with little to no skill, will neutralize an opponent.  If I feel my life is at risk, I will use whatever force I feel is necessary to protect it.  A person cannot be squeamish about self-defense.  Street fights are not honorable or fair.  They are quick (quicker than you will expect by far!), brutal, and sometimes tragic.  Plan to be the person able to walk away.  Eyeballs are gross.  Digging your thumb into one is doubly gross.  But I'd rather be grossed out than knocked down, kicked in the spleen, and bleed out in an alley.  You should know your local laws about necessary and proportionate self defense.  Make your own choices, but make them now before you find yourself having to make them in a situation where hesitation can cost you your life.
7. Punch correctly.  Close your fist.  Your thumb should be on the outside of the clenched fist, no finger or thumb should be extruding from the balled fist.  The wrist should be as straight as possible.  Find a cushion lay it upright against something hard, like a wall, and punch as hard as you can (graduating up in force, not all at once).  You should not feel your wrist buckle.  You should not feel your fingers roll.  You should feel nothing but your own palm at the ends of end finger.  Nothing should touch the tip of the thumb.  You should hit with the "bottom three" knuckles; that is to say, the middle knuckle through the pinky knuckle should hit flat against the wall through the cushion.  Don't "knuckle punch."  You'll regret that in a real fight.  Punch straight.  No roundhouses, unless you don't have a choice.  Jab and step back.  Follow up instantly if the first punch slows the aggressor down.  If the aggressor appears to be losing, don't stop until he has stopped being agressive.  Personally, I won't stop until he is physically incapable of being aggressive.  Let your own judgement and the local laws tell you when you should stop.
8. Don't kick.  Just don't.  Stomping is good.  Kicking, unless you are trained, is stupid.  If you must use your feet, stomp the tops of your opponent's feet and kick with your instep no higher than the shin.  But really, just don't kick.
9. Bite but don't scratch.  Bite hard.  It will hurt them.  Scratching will just piss them off.
10. Stay on his strong side.  If he is right handed (his right hand is cocked back when his guard is up), stay on his right when possible.  Don't give him room to swing around.  Do the opposite if he's left handed.
11. Use objects.  A pen, a bottle, and chair.  Who gives a damn what it is?  If it'll hurt worse than your fist, pick it up and hit him with it.  Expect that if you don't, he will.
12. Get away as soon as you can.  Don't stick around if you don't have to.  If the door is open and you can leave, even mid-fight, do it.  Don't take your eyes off your opponent, but always know where the exit is and try to keep the path to it clear and straight.

There are a ton of self-defense classes that will show you techniques for getting away, pushing a person down, breaking holds, and other things.  There's nothing wrong with that, but a real street fight isn't about cool technique or slick moves.  It's about taking a punch and giving out punishment until someone stops the fight.  I'm a big fan of technique.  I've studied Tang Soo Do, Kickboxing, Aikijutsu, Aikido, and Jow Ga Kung Fu.  I love technique, and in experienced hands, it's a game changer.  If, however, you are reading this to learn how to win a fight, you aren't experienced.  Stick with the basics.  If you can take a hit or two, know how to punch, and are willing to go for the eyes and throat, you stand a decent chance of winning your next fight.

If you are interested in learning more about the martial arts, consider looking up schools in your area.  Wing Chun is an effective street style, as are Krav Maga, Ju-Jitsu, and Jeet Kun Do.  Most any martial art will work, though, as long as the teacher is reputable.