Use different weapons and levels of terrain.
Do you have a battle prepared with bandits on the road?
Sounds simple. And boring.
Instead of all the bandits lining up and using swords, have a few bandits in up the trees. Having archers shooting down onto the party adds a new level to the combat.
Players will have to defend from above and below. Have the same types of enemies use different types of weapons. Place the battle on multiple levels of terrain.
Use more magic.
Place a bandit who is hiding in the trees with a wand of magic missile to shake things up.
Spell casting can add a lot more obstacles to a simple battle.
A bad guy can cast entangle or a fog cloud.
Some more powerful enemies can heal themselves with potions and magic.
Letting the enemies use magic will always be more memorable than a couple grunts with swords.
Use Traps.
Maybe the bandits placed traps in the road for the players to avoid or disable.
The terrain itself can end up being an encounter on its own. Use traps, pressure plates, caltrops or simple trip wires to slow the players down.
Getting attacked by swords is fun, but a sword fight where you have to avoid traps is a lot more engaging.
Maybe the players will have to get around a cloud of poison gas. Get through a couple locked doors.
Have spike traps that pop up every other round or a magic trap that damages players every turn until a puzzle is solved.
Use The Environment.
Make the land itself more exciting. Fighting bandits on the road in the forest? Good start. Perhaps the road is now on the edge of a cliff, or the bandits attack on an old bridge.
Maybe the fight takes place in the fire swamp where everyone will have to avoid quicksand and fire traps.
How about a duel inside a building on fire with the roof crashing down on the combatants. Maybe a cave is collapsing around you.
Diversify your monster types.
Have monsters with different abilities fight alongside the bandits.
A sword fight against bandits just got weird when one of them changes into a werewolf.
Maybe the fight disturbs a nest of giant spiders or an owl-bear. It's not so simple a sword fight anymore when some wood nymphs are trying to protect their trees.
The fight with the wizard just got more complicated when you find out he has an ogre body guard or he commands a tribe of knolls to fight for him.
Add Personality to your bad guys.
Make the enemies more human and relate-able.
Give all the random bandits some names.
John and Erin get sad or angry when they see their comrades die in battle.
The enemies can talk to the players on their turns and try to make deals.
Maybe they decide to run away and get revenge on the players later.
Maybe the bandits were just following orders and don't want to get killed in a random battle.
When a goblin gets killed, another one suddenly cries out, "Gratz! Don't die today! you are my only brother!"
This is great for adding detail and world building. They aren't just random enemies anymore when they have thoughts and feelings.
The NPC's aren't just simple meat for the grinder. The best battles will mean something to somebody. Including enemies.
During the obligatory tavern brawl, the players might have accidentally killed the daughter of a nobleman. Now it's not just a random bar fight, its part of the story.
-The players will have to figure out what to do when the guards come asking around.
-The nobles could do a lot to try to get revenge.
-They could send assassins to kill the players.
-The nobles could outlaw weapons and magic items throughout the land.
-The players could get arrested for murder.
Put more obstacles in the players way.
The players might need to solve a puzzle or get past a magic portal or gate before they can kill the bad guy.
Make the players fight through a few waves of enemies before they reach the boss.
Give the big boss a shield or force field the players need to take down before they can hurt him. All while the boss can still hit them.
Make the players cast a ritual spell that takes more than one turn to cast.
Give the players an objective that is different from just killing enemies.
The party needs to get the contents of a treasure chest before the bandits do.
The players might need to solve a puzzle or get past a magic portal or gate before they can kill the bad guy.
The bandits could have hostages that the players need to save.
Maybe a bandit is using a weapon or magic item that the players need for their quest.
The players could be tasked with stopping an evil cult from performing a ritual before time runs out and the bandits are in the way.
Create some kind of time limit will make a battle more intense. They only have 4 rounds before the magic orb explodes.
Save the hostages before they get killed.
Stop a magic artifact before it burns down the whole forest.
Add narrative flavor and to the attacks and movements.
focusing on the numbers can get boring really quickly.
Explain why the goblin rolled a 1 and missed his attack.
He just saw his fellow tribesmen get slaughtered by the PC's, of course he would get a little rattled.
If a roll is close but doesn't hit, talk about how the arrow hit the armor and bounced off.
Talk about how the player was just an inch away from dodging a sword to the face.
Everyone likes to explain in detail how they hit a guy. Describe the misses too.
Make it personal.
If you have ample time to prepare an ongoing campaign, make each encounter personal to the characters back story or the goal of the current mission.
A player is on the way to find their missing brother?
Erin the bandit used to work with the missing brother and has info on him.
If you are a good DM you can make this stuff up on the spot.
Have the characters talk during battle. John the bandit might know the location of the lost dungeon the players are looking for.
The missing brother could have owed money to the bandits or there was a secret love triangle with some of them.
If you plan this well, you won't ever need random encounters. The villains goals can be just as much a part of the story at the players.
You don't have to add all of these things to every battle of course, that would make things complicated very quickly.
Help out and communicate with your players.
Give players hints about monster resistances and other special abilities.
The game will go slowly if you have skeletons who resist piercing damage and all the players are using swords.
Let the players notice that the swords aren't effective.
Have them roll perception checks or knowledge checks to realize that a hammer or club would do a better job.
There is no need to waste your players time.
Don't let the battle go on forever when each player is only doing 3 damage.
Players will appreciate the help and feel more accomplished when they figure stuff out. but you have to give them clues.
Characters have a lot of abilities and sometimes players won't know about them, or won't know what they do.
It is your job as the DM to give hints and suggestions.
Have more experienced players help out the group to free up your time.
Speed up the battle.
Delegate everything to your players to make the battles go faster.
Have a player keep track of initiative for you.
Have a player check the stats of each other character so the players know what they have.
If you have a small battle with goblins that are not imperative to the plot line, have a player keep track of the goblins hit points.
This gives you extra time to plan on whats next, or role play a conversation during battle.
Have players draw maps for you.
Ask for a players help to move around minis and other game pieces.
Most players are always willing to help, and you should let them. It frees up your time and the players feel more involved.
Tell players that you expect them to know what dice they are rolling and what modifiers and bonuses to add.
The DM should take time at the beginning of the game to help players out so it will run smoothly later on.
If players are ready and know what they are doing, you can shave off some extra time in battle. Have players roll all their attacks and damage dice at the same time.
I have a way to use initiative that speeds up the battles and helps communicate whats going on in my games. Maybe you should ask about it.
