1. Be sure the reader has no clear idea of who could win.

Don't make one side so much stronger than the other that the fight is simply an easy win. Even if one side is overwhelmed, there's got to be some element that keeps hope alive - that gives the reader uncertainty as to what the end outcome could really be. Could the enemy really win? Could the hero win?

Where most of us make the mistake with this one is making the hero so strong that the villain loses far too easily. Remember that it is important to make strong and intelligent villains to make your story more interesting and give that hero a challenge. (I would even argue that the villain needs to be smarter than the hero, but that is my opinion.)

2. Build it up, and bring it down.

Fights don't usually come out of nowhere. Fights start building chapters in advance, sometimes. Yes, there may be an ambush, but the actual foreshadowing for that fight should come long before. The reader needs to know that there is a fight coming, that there is conflict brewing. We don't have music like a movie would to inform the readers of the tension, so it needs to be created. Shadows, atmosphere, interaction - all of those things can hint toward what could be coming.

And don't forget to bring it down once the fight is done. Let the reader take a look around and see the results - destruction (if any), bodies, blood, weapons, clothing, sweaty foreheads - anything that may have been affected.

3. Cut the conversation.

People don't really talk when fighting very much. Their adrenaline is pumping, their breath is getting knocked out of them. Unless they are Jackie Chan, they aren't going to be making impressive comments when getting thrown across the room into a wall. Make the scene about the fight - show, don't tell. Describe the sensations around the fighters - what are they feeling, how does it smell, are they tense or relaxed? There are so many ways to communicate how they feel without resorting to panting words.

4. Make the sentences a bit shorter.

You want the reader to move at a quick pace, to simulate what happens in a fight. (A slow fight isn't as interesting.) Longer sentences are great for description, but can slow down the pace of the fight by quite a bit. It might take some time to create the delicate balance between getting that description in and getting the right pace, but it is well worth it.

You can definitely make your sentences longer again once you are describing the aftermath, as mentioned in #2. The pace afterward is more relaxed, so the lengthier sentences will help the reader slow their own pace a bit to match the new pace of the scene.

5. Make an outline.

I know, I know. Outlines can be quite the pain. However, if you create an outline and follow it, you can make sure the fight scene goes exactly where you want it to. Fight scenes can get out of control fast, and an author can lose where they meant to go in the description and excitement. (I swear they are just as exciting to write as they are to read.)