
Action Movies: Youtube is your friend here (and I don't say that often). Search up action scenes from the good action flicks like Elektra, the Matrix (all three), and so on. These fight scenes will help you come up with description. Especially if you know absolutely nothing about fighting.
Kick-ass Music: This is not necessarily crucial, but it works for me. Awesome, loud, rock out music really helps with writing the action scenes. It helps me get into that adrenaline high mindset that (I imagine) a person going into a fight might have.
Choreography: The stunt directors in the movies do it and you should to. Go in with an idea of who's fighting who, how, and when. Even if you're not going to write a play by play, have it in your head. It's super super helpful to know exactly what's happening so that you can transfer it better to paper or screen. Really. Honest. No lie.
Write, write, write: I know this seems kind of obvious, but when you're stuck in the depths of despair it isn't. Once you've got the music, done your research and mentally choreagraphed the action scene write it. Write it however many times you need to get it right, but get it down. You'll notice what's wrong and what's not working. But if you never get it down, you'll never get past the scene and get to write the rest of the awesome stuff.
That's pretty much all I could think of to help with writing these tricky scenes. If you guys have suggestions of your own, please share. The rest of us would love to hear! :)
*The image above belongs to tower-raven of Deviantart.*