- Beware of the action/reaction/action or the back-and-forth pattern. When writing fight scenes, it's so easy to fall into a back-and-forth pattern. Hero makes a move. Villain counters. Hero makes another move. Villain counters again. This is repetitive, and boring to read. If you watch the below videos (especially the second one), you'll see that fights like this are not so much back-and-forth, and there's more flow to it. Vary the pattern.
- Keep a narrow focus with your narration. Keep in mind the things your character will be thinking about, will be seeing. If Hero is in the middle of a duel, he's not going to be looking up and noticing the landscape on the horizon or some birds flying overhead. His focus will be much closer: the sweat on his forehead, the breathing of his opponent, the feel of the gravel beneath his feet.
- Consider all senses. Sight is the most heavily used sense in narration, with hearing a close second. Why limit yourself to these two? Don't forget to think about what your character is physically feeling, smelling, or tasting. Did Hero fall on the ground during the fight and get a taste of dirt? Things like that. Utilizing all the sense can turn a mediocre fight scene into one that comes to life.
- Consider terrain/surroundings. (Both of the below videos have nice examples of this, especially the Princess Bride one.) If your fight takes place on a flat piece of grass, it's going to be very different from a duel that happens on a mountaintop. Keep in mind the surroundings when writing the scene, and use these to spice up the action. Hero has to worry about Villain's blade coming after him, and falling off a ledge? Things like this make everything more interesting.
- Please, please, please don't have your characters lugging around twenty pound swords. I already ranted about this, so I won't go into too much detail. Do your research, and find that swords actually were not heavy. More info on this here.
While I'm at it, here are some rather nice duels. The first is between Jack Sparrow and Will Turner in The Curse of the Black Pearl, and the second is the Inigo/Dread Pirate Roberts one from The Princess Bride.
What are your tricks for writing fight scenes?