Be ready to block

The big right hook is by far the most popular strike thrown by anyone.  Other common moves are headbutts and low kicks.  You may come across someone who has done a minimal amount of training in boxing, then you also have to look out for jabs, crosses and uppercuts.  These are the most common strikes thrown by any street attacker but don't be surprised to see anything else coming your way.  Keeping a good guard up at all times is crucial to staying safe in a street fight.  Keep your hands high because most punches will be to the head.

Landing strikes

Hitting someone in a real fight is much harder than hitting pads or a sparring partner because nothing ever goes exactly the way you expect it to in a real life situation.  Moving forwards is usually the key to landing strikes in a fight.  Keep your enemy on the back foot and move forwards into every strike that you execute.  Also throw combos, never assume that a single punch can end the fight.  Keep on punching until your enemy is on the ground and then make sure that they won't get back up again.

Distractions

Causing a diversion can be effective in a street fight.  Spitting into someones face, throwing loose change, shouting down someones ear, you could pretend to be drunk or you could pretend to be terrified.  Anything to trick your opponent and catch them off guard.

Squaring up

Most people will square up to you before they start throwing punches at you.  This is because they are deciding how tough you are and if they will get hurt if they fight you.  This is a great time to attack because your opponent still hasn't decided weither they should hit you or not and they will probably be caught off guard.  Failing that acting like you are tough and want a fight may make your attacker think twice. 

Grappling

A lot of fights go to the ground if they last for long enough.  If you're only fighting one person that's fine, but if you have more than one attacker try not to use any grappling techniques which go to the ground because you might get kicked in.  Having said that most people who will attack you in the street will probably be least experienced with close range fighting.  Getting right in someones face will probably increase your chance of landing a great strike like an elbow.