Move The Story Forward

The very first rule for fight writing (and writing any scene in general) is to ensure that it moves the story forward. Say "no" to gratuitous fight scenes that only show off fancy moves or writing skills.

Here's the easiest way to find out if your fight scene moves the story: Delete it. Now, read the scene before and the scene after. Can you still make sense of what happened? Is the fight scene essential to the overall plot or story?

If the fight caused some type of transition in your story, keep it in.

And remember: Not all transitions are physical. Some are mental. You don't always have to discuss the physical aftermath. You can also explore the mental fallout after a fight. This can be how the fight moves the story forward.

Also, It's more fun and interesting to have both/all sides make sense. If one side is particularly stupid, it's not that rewarding to read. (But I guess this doesn't apply to all fights.)