Break up fights calmly.
If you add excitement and screaming then they can fight more. I usually watch and step in if there is a slight break. Generally dogs aren't biting hard, they are just snarling, and using aggression to win the conflict. So they get excited and you show them you are cool.
Basically to avoid it you need to stop the lead up. Any posturing, growling, baring teeth, barking, getting in each others space should be stopped. In my opinion a dog should be allowed sit in peace with out any other dog picking on it. Sometimes dogs can't defend themselves so you need to do it.
Always consider who is starting the fights. Then stop them and what ever behavior is triggering the fight. The behavior the other dog is doing to protect itself should be allowed to a degree. If it is shown you are in control of the situation it shouldn't need to protect itself.