Now when you see two cats fighting, one thing you might do is to pour
some cold water over them . A good soaking will usually break up the
fight. Never reach into a cat fight.  I've made that mistake and both
of them turned on the "peacemaker."  Needless to say, my tetanus shots
were up to date. Whatever you do, don't hit them with brooms,
newspapers or any other solid object, even if your cat is the one
getting the worst of the situation.  Most of the time that only makes
both animals more aggressive and once again one or both may turn on
you once they identify the fact that you are the one holding the
broom.

If you have a cat fight on your hands and don't have any water
available, make a loud noise such as clapping, banging a pan, etc. 
Cats hate loud sudden noises and it often will end the confrontation.

One of your cats may smell funny to the other.  Sometimes it may take
three or four months to get one cat to accept the scent of another as
'normal,' and will continue to fight till that situation is cleared
up.  However, there is a way to clear that up a little faster.  First,
rub a towel over one of the cats.  Then rub the same towel over the
other cat.  Now the cats will smell (kinda, sorta) the same and peace
can be restored.  That is the reason kitty never attacks the cat in
the mirror after having seen a reflection once and checking it out. 
The cat in the mirror has no scent.

Some people with more than one cat never have a problem with fights,
but others find that their cats are always getting it on in some arena
or other. One reason cats in the same house fight is that there isn't
enough "territory" for each.  It's not a question of square feet. 
Each cat has his own internal sense of space. In order to satisfy each
animal's need for a separate territory, try repositioning a large
piece of furniture.  In other words, rearrange the furniture so that
it breaks up a large space, creating two or three smaller areas. If
each cat has a space of his own, it may put an end to the fighting.

You can create more separate cat spaces in your home by setting up
decorative paneled screens which are available at most furniture
stores.  Set one up in a corner to create space front and back.

You can buy a "cat tree" which will perform a similar function.  Cat
trees are tall towers with several carpeted shelves.  When you bring
one of these trees home, each cat will usually adopt a shelf as its
own.  Since the cat then has "its own" space, they are less likely to
fight over territory.

Now if you have tried all of the above and nothing works, you may find
out that by constantly breaking up their fights, you are merely
prolonging the situation.  That's because what they are fighting over
has never been settled.  It may (and usually is) fighting over who is
to be top cat.  And cats don't have any sexist chauvenism.  The "Top
Cat" can be either male or female.  In that case, settle your nerves,
and let'em duke it out as long as they aren't getting torn to pieces. 
A few nose scratches are minor.  As for losing an eye, cats have been
fighting for a few million years and one eyed cats are still rather
uncommon.  The adds are strongly in your favor that one or the other
will cry uncle and submit before either one gets seriously hurt. 
After they have established their boundries (on their own), the
fighting usually ends completely.