Say you're a character in an RPG group. If you are the group’s brawler, your moments of triumph will clearly happen in combat. You have designed the character to enhance the experience of a fight into an epic battle. This person will save the world through strength and skill; they are able to slay legions of foes and go toe-to-toe with the most monstrous fiends. It is an all-too-common tragedy to see these characters forced into dull fights by a GM unwilling to spice up a battlefield.
Of course, that’s a tall order for a game master. Making enemies is an art requiring a deep understanding of the game mechanics. Even if the system has premade monsters and level recommendations, the specifics of your party can make drastic differences: an opponent which would slaughter a platemail-clad warrior could fall effortlessly to a sorcerer with the right spells. What you can do as a novice GM, is follow some general guidelines to ensure a better overall experience.
The two mantras I maintain when planning a fight are “players should be able to lose” and “players always do better than you think”. Design the encounter to push their limits. Try to kill them every time, though spread out the damage across the whole team to keep everyone up and participating. Knocking someone out makes tactical sense, but is really boring to the player on the sidelines. By having more powerful adversaries, you can pull your punches and make less than ideal choices while still challenging and intimidating players.
Along with having strong enough foes to put up resistance, making the enemies diverse and numerous lends a natural challenge to the fight. Experiment with your limits as a GM and the system to see how many NPCs you can handle: a barrage of arrows from all angles is a thrilling introduction for a combat encounter. Having multiple targets also prevents stuns or incapacitating abilities from being too powerful; you want skills your players chose to affect battle, but not result in instant victory. The same goes for providing different opponent archetypes simultaneously; let a player feel overjoyed about perfectly countering an enemy while being afraid of his weakness about to disable them at any moment.
A battle is not just the combatants; it is the field as well. Do not put players in an empty rectangular room. Give them cover and obstacles. Go three-dimensional. Make things to interact with like cars, drawbridges, explosives, spike pits, or whatever works for the setting. Add one-off special mechanics to make a scene really special. One of our Catalyst demo sessions involves the players’ boat chasing alongside a horrible, demon-carrying warbeast. Every couple of turns, the drivers of each transport must make a driving check to stay in control. The first batch of players won by having a character magically jump from the boat onto the beast, fling the driver off to his death, pump the beast full of buckshot, and (gracelessly) hop back into the boat as the creature slumped to the ground in defeat.
Defeating your foes in glorious battle in supposed to be an unrivaled feeling. Let your players experience that. Provide worthy foes in magnificent arenas. Make your warriors earn the respect of those they fight to save. Or kill them in the process; maybe they needed to learn a lesson about overconfidence…