Making Combat Interesting in TTRPGs
Combat Should Be More Than Hit Points
Combat is a huge component in a lot of TTRPGs, especially D&D, but it can often feel like a slog which bogs down the pacing of the game to roll some dice and watch some numbers go down. Combat should be more than just piles of hit points being checked against the damage per round, and this is how I try to make it so.
Use the Environment
First up on the turn order is environmental conditions. Any fight can be leveled up in complexity, challenge, and intrigue by simply adding in a component to the environment in which the fight is occurring to spice it up. In cases in which the players are fighting something on its home field, which is more common than not, those creatures should gain some kind of advantage from their environment against the players.
For example, imagine you have a barbarian in the party that always charges the least armored opponent in every encounter to burst them down, leaving the encounter neutralized because the powerful mage dies too quickly. Now imagine that exact same encounter, but you utilized the environment to introduce interesting variables to the situation. That same mage is the same distance away, but now there's mud between the barbarian and the mage. Difficult terrain makes it so movement is effectively halved, and things like charging just cannot happen without special effects. The encounter goes from a quick and unsatisfying fight to one that requires the barbarian to reposition or find a creative solution to deal their damage to the mage.
Another way to utilize the environment is verticality. Flying creatures, archers on ledges, that kind of thing. With verticality, the players need to figure out how to hit the enemy and how to defend themselves in new ways. Make your players need to use a Fly spell, find ladders, stack boxes, or get creative.
Lastly, there's the simple environmental factor of cover. Cover can be extra interesting in many of the same ways that verticality can, but it also adds a lot of mechanical oomph. Cover can affect area-of-effect Reflex saves, allow creatures to use their Hide skill to deny Dexterity to Armor Class, and even provide a massive bonus to Armor Class. Not only is cover mechanically rich, but it can affect players as much as enemies, so let your players take advantage of cover they've wrested from the control of their opponents as they turn the tide of battle.
Run Intelligent Enemies
Another way to spice up an encounter is to have enemies that just plain don't want to die. They use tactics like flanking, and they utilize items that a player might, like tossing oil on the ground to put the players off balance. They could form a phalanx in front of an archer or a mage to create a problem where players have to find a way around the front line as soon as possible.
Maybe a big brute does a grapple attack and walks into an area of effect that it can survive just to deal more damage, think of a demon walking into a fireball. These enemies aren't just stat blocks waiting to be hit until their HP is 0, they want to win as badly as the players.
All of these tactics also affect the action economy. If an enemy can force a fighter to spend an entire round climbing, standing up, or escaping a grapple, they've effectively stolen that turn.
In the same vein, just like the players, they don't want to die. That means not every battle needs to be to the death. It's okay to have enemies who surrender, throw down their arms, give up secrets, offer to help the party, and more.
Create Meaningful Danger
My rule of thumb with combat is that if the players are fighting something you set up, they should feel as though they can die. Not that they should die in every encounter. Not every fight needs to feel like a meat grinder that eats up player characters.
Instead, it should feel like if the dice go one way, the fight can be relatively easy, and if the dice go another, the players might be on death's door or eating dinner with 'em. This kind of mindset encourages your players to use the things they have, use their environment, and use tactics to win.
If you're tired of hearing, "I swing on 'em," every single turn of combat, then make your players feel like swinging on 'em isn't good enough for every single turn of combat. It'll be more engaging for your players, as they'll be wondering what options will actually work to get them out of bad fights, and it'll be more engaging for you as you get to play out a more sophisticated sequence than telling people it's their turn to roll to hit.
Manage Resources Across the Adventuring Day
Another important piece of the puzzle of combat is that, with certain exceptions like big boss fights, you should look to run multiple encounters per day.
D&D at its core is a resource management simulation. Hit points, gold, potions, spell slots, allies, actions per round, there's a resource at every turn, literally. Look to make your players make decisions about how they spend those resources.
Is it worthwhile to spend a high-level spell slot to end this encounter sooner if the party doesn't know when they'll be able to rest next? Maybe it's better to lose the HP now and hold that spell in case there's something scarier around the corner. Decisions about healing versus buffing matter much more once the party has to conserve resources across several encounters.
If you're only running one encounter per day, or tragically allowing your party to rest at every available moment, then you're letting precious tension go to waste. Put pressure on them in creative ways, like a constantly roaming monster that's not possible to kill, think Mr. X from the Resident Evil 2 remake, so it's tough to stay in one place. You could also use a constant hum that prevents them from sleeping, or even a simple dungeon-wide effect that deals 1 damage per hour and prevents them from getting in their rest period without significantly harming them.
Let Your Players Feel Powerful
The last component is more flavor than crunch, but let your players feel cool. Let them kill enemies how they want, and encourage them to describe their attacks. Not every sword swing is the same, not every fireball has the same effect, and it's your job as the DM to translate these numbers and descriptions into the minds of your players.
An effective rule I use in my games is that if my players overkill an enemy by 10 HP or more, they get to describe their kill. This makes it so not every attack needs to be described in painstaking detail, but finishing blows with power behind them get a fun burst of flavor that makes your players feel the power in that blow.