Rule 1: This is a no brainer, but the fight must be fought with fists and nothing else, ie no special powers. Even if giant robots are the main combatants in the show, they must settle their differences outside of their robots in the end. And by no means does this mean the fighters will find their weapons in the end and preform the coup de grace before the enemy can; fists all the way baby.
Rule 2: This rule is very important, no one fighter will have the upper hand; both must be equal in every way. We in the business call this exchanging blows.
Rule 4: This is one rule that has to be enforced, because it kills so many other fights. NO TALKING ! By this time the characters are at a point when talking is over, now the only talking they will be doing is with their fists.
Very few anime have done this right, and when it is done right it is amazing. Gurren Lagann: Lagann-Hen pulled it off perfectly, S-CRY-ed also did a great job of it as well. After watching those, can you imagine what other anime would look like if they settled their differences with good old fashion fisticuffs?