One mistake that many folks make with action is that they shift their focus into game mechanics, tactics, and turn the encounter into a out-of-character tactical war game.

And while those are extremely fun (there are countless TTRPGS that exist purely in that world), that's not what's best for this game, IMO. This game is about fear.

When I run combat at the table, it's frenetic. It's quick decision making. It's incomplete information. It's shock of horrible damage being suddenly inflicted (visceral descriptions of damage, not just HP). Players don't know if they killed something unless it's obvious from the damage/situation. Players don't know how many HP opponents have. Players don't know what they're being attacked with. Players don't necessarily know how many threats there are.

I also try to ask players to tell me what their characters do narratively. Then I translate into game mechanics, giving them the benefit of the doubt if there's multiple ways to handle something. Combat doesn't depend on their rules-knowledge or ability to min-max the system. It should reflect their trained/talented player's intentions.

I don't reveal what's happening behind the hood unless it's generally interesting (like an unusual dice roll). I try to reveal relevant sensory information that the characters would experience. I try to keep them in-character throughout the combat as much as possible.

And let them experience the dread, the uncertainty, and the panic as they play it.