When I write physical fights like a sword battle, I picture the fight like it's a movie. I see what each character is doing and what is happening around them.
I also get up from the computer and pretend I'm holding a sword, imagine the opponent's move, and block it noting my balance, what I'm leaving open, and the possible return blow.
To vary the fighting, I use the physical location of the hero. The floor may be bloody from his first opponent so the hero or villain may slip and fail to parry a blow, etc. If more than one good guy is fighting, the fighters may affect each other as an enemy steps into the hero's range, or he falls beside him.
I rarely write out blow for blow because I think that's boring. Instead, I'll give occasional overviews of what's happening while staying in the character's viewpoint. For example, the hero is thinking about how his body is learning the rhythm of the fight, or he's aware of other fighters around him.
I try to avoid using technical terms to describe the fight because I'm writing as much for those unfamiliar with swordplay as those who are, but I try to be accurate about how to use the weapon, and I use a sprinkling of correct terminology to make it seem more realistic.
I've never fought with a sword, but I've held a number in my hand, and I've watched others fight with them. I try to remember the weight of the weapon, the sound a fighter makes as he swings the heavy sword, and the sheer weariness of the weight of fighting something or someone above you.
I also include different senses in the description. What is the character hearing? Feeling? Smelling? Tasting?
This method also works with fist fights and other man to man combat.