I talked a little bit about this idea in another post (HERE). This time I will focus on making encounters work in a wuxia campaign (and in particular how they work in my Wandering Heroes of Ogre sessions).
Though Wandering Heroes of Ogre still has fantasy elements, allowing for encounters with supernatural creatures like Fox Demons and Hopping Ghosts, it is basically rooted in human-driven wuxia, so most of the opponents the players face will be other people. If you don't mix things up, and if you don't consider how to make encounters stand out, they can easily become too familiar. I use a lot of random tables to make sure that doesn't happen, but some encounters I know will occur in advance (for example when the party incurs a grudge with a sect, it is likely the sect members will stage an ambush on their own terms). These observations apply to both situations, but particularly the latter, where you have more time to put a memorable encounter together before it occurs.
Two things really need to stand out about your NPCs in an encounter with martial heroes: physical appearance and combat abilities.
If the players are facing off against four different Kung Fu experts an easy way to make them memorable is to give each one a strong physical characteristic. This can be in the form of clothing (a turban, a large golden medallion, a fine silk robe, heavy black armor, etc) or appearance (an ugly face, a big beard, a bald head, an enormous and hefty body).
Once combat begins, make sure you've selected appropriate combat abilities for them. In Wandering Heroes of Ogre Gate this means giving them one or two solid Kung Fu techniques that reflect their character well and make a lasting impression. You will want other standard techniques also, but it is just really important to give them at least two signature moves.
Another thing you need to know is personality. This is important because not all encounters end in combat and even those that do, often allow for some kind of social exchange. It is also important because you need to know how the NPC reacts to unexpected things, like offers of compromise by the player characters.
I try to give NPCs in these kinds of situations one or two strong personality traits. The purpose here isn't to know their life story (though you may want that if the character survives the initial exchange) it is mainly to know how they conduct themselves in combat. Are they fair? Do they show mercy? Do they pay for the damage they cause? etc.
Beyond the NPCs you also need to consider location. This is crucial in a wuxia campaign. This isn't just where the fight takes place, but how it occurs. Sometimes the characters just bump into the wrong people on the road and a battle ensues. However you want to make use of the setting and the participants to keep it memorable. If the attackers are planning to strike the party, they probably don't just walk up to them on the road (though that can certainly happen). At the very least they are going to go in with a plan. Let them use some tactics. Maybe they lure the players somewhere they know they'll have the advantage, or perhaps they approach the party as friends or allies to get them to lower their guard and strike at an appointed time. Make good use of inns, restaurants, festivals, temples, markets, bridge crossings, and other key locations.
If it is an encounter of random chance, even just a passing each other on the road kind of exchange, give the opponents purpose and root them to something. Their not just passing the party for no reason, if they are on the road, they have a reason for being there. Maybe they are transporting a body from a rural village to a city (or vice versa) and in their grief they are itching for a fight. Perhaps they are looking for bandits who stole their father's prized golden sword (and the PCs happen to resemble them). Think of why they are there and if it is a hostile encounter, decide why they are hostile toward the party.
I'll probably talk a little more about this after my next session (when I can discuss some concrete examples without giving away too much to my own players).