One of the things that tends to be associated with urban fantasy is action/fighting. If Chekhov is going to show off a gun in the first act, you can be damn sure that it’s going to go off by the third act, and if this is an urban fantasy that you’re talking about, that gun firing is probably going to be intentional.
You’ve probably seen quite a number of action movies with sweet fight scenes in them, and the natural inclination–it was certainly my first inclination when I began writing seriously–is to try to reproduce that sort of carefully-choreographed fight scene in your writing. The problem with that is that words are not pictures, let alone moving pictures, and it can be hard to translate something you see perfectly well in your head onto the page in such a way that others will see the same things you imagined.
One thing to be sure of, if you have a big fight scene, is to have clear blocking–that is, where everyone important is standing/crouching/lying. As in the days before it was assumed that you’d be playing D&D with minis, it can be hard to tell readers where everyone is during a fight. All too often, you may have a character standing in one place, very near an enemy, but readers may imagine that character standing somewhere completely different. While you’re trying to make your blocking as clear as possible, you must also keep from bogging readers down with information that gets in the way of the action. You only need to describe the blocking of a scene when it’s very important to know where everyone is; otherwise, you may give broad-stroke information, painting a fight that everyone can imagine without having to tell them “look, here is where the protagonist is, and there are grunts crouched behind barrels here, here, and here.”
As an example, here’s an excerpt from an early draft of an urban fantasy parody that I’m working on:
The sound of the door slamming open was drowned out by the roar of gunfire which accompanied it. The dim warehouse was illuminated by the strobe of muzzle flashes migrating about the floor, going from cover to cover. Sasha had dived behind a huge, disused lathe as soon as she had breached the door, and her Glock chattered out streams of slugs as the thugs shooting at her broke from cover, trying to flank her.
Between bursts, she scanned the room, looking for the shadow of Jack. He had charged in before Sasha was even in cover, his form melting from that of a handsome man and re-coalescing as a large wolf, and he was on a tear. Sasha could only catch flashes of him, but she could hear the results of his work in the screams of the blood-slaves who had been lounging about the warehouse when she and Jack had burst in.
Looking around, Sasha locked her eyes onto the lit window of a small office along one of the warehouse walls. Sasha knew that was where Vladimir’s under-boss, Agrippa, was. She began plotting a route through the room, looking for the shortest distances between pieces of cover. Then, with half a plan in mind as the confidence to make the rest of it up on the fly, she burst from cover, spraying the room with lead for the few seconds that she was in the open.
Crouched behind another piece of heavy machinery, Sasha checked her equipment, noting that she had only a few more loaded clips for her Glock. Holstering the handgun, she unslung the shortened Ithaca pump-action from its place under her trench coat. The next piece of cover was a bit farther away than she had first judged. She peeked around the side of her cover, spotting Jack a dozen yards away, his bare, now-human chest heaving as he crouched, rifle in hand, behind a stack of boxes.
In this example, I’ve communicated all the essential details about the scene without having to give a full layout of the warehouse because readers can imagine what the inside of the warehouse looks like without my telling them every little detail.
There is equal danger in bogging down your readers in a blow-by-blow fight scene. As is the case with slow pieces of dialog, slow, boring blow-by-blow scenes are better summarized. There are places where blow-by-blow fight scenes work well, but they’re often better avoided.
The folks over at Writing Excuses did an episode on this topic a while back which I recommend.