The big fight scene is often the pivotal point of a story.  It can literally make or break your entire work.  If you have spent thousands of words, chapter after chapter, leading your reader to the ultimate point of conflict, you need to deliver the goods.

Here are a few tips for bringing the fight from your imagination to the page.

*Know your terms.  If you are fighting with swords use the right sword terminology.  Scimitars don't move like katanas.   The same goes for any other weapon real or imaginary.
*Find more interesting ways of saying punched, hit, or slapped.
*Keep your fight physically possible.  Make sure you follow the rules of your world.  Act out your action if you need to.  Friends love to help with this over free pizza.
*Never "discover" a never before mentioned ability.  If your character is going to use some cool technique, the reader needs to know about it in advance.
*Never "find" a way too convenient weapon.  Make sure your reader knows what is available to be used.  Conversely, don't show the reader a weapon and not use it.
*Keep your characters in character.  If you have a shocking twist, make sure the reader has enough information to enjoy your hard work.
*Have a lucky volunteer, more free food, read your scene out loud to you.  If they can't make a smooth reading out if it, don't try to correct them - you have more work to do.

Practice, practice, and do more practice until your fights make sense and flow smoothly.