I run a mixture of theatre of the mind combat (where there’s no map) and and combat with maps and minis (or virtual tokens as the case has been lately). I like both and would generally prefer theater of the mind, but my players often prefer the latter and I think that’s because I forget about vision during combat.
What do the player characters see? What is blocking their vision? What’s impairing their vision? Maybe it’s very dark, or smoky, or foggy. Maybe there’s something very bright in the room that makes them look away. Maybe they’re fighting a medusa or basilisk and need to look away. If the players don’t know that they’re looking at, they’re generally going to ask what’s in front of them and hit it with whatever they’ve got. For some combats, that’s going to be okay. However, try to keep that a rare occurrence and think about what they would be seeing in the situation:
Dust swirls around in the antechamber as you push aside the slab door. It’s hard to see more than 10 feet, but you catch a glint off of something every few seconds. It goes from the left to right with an unnatural and unerring cadence.
The airlock swishes open and you’re looking into a well-lit, tidy interior devoid of life. You’re scanning the scene when a small canister lands in front of you and the flash bang ignites right in front of you, blinding (and deafening) you for a few moments as you’re roughly handled by someone who wasn’t there moments ago.
Remember to use their vision, but purposefully take it away sometimes too.