Ah. White room syndrome. It’s a very normal thing because as writers, we tend to see things perfectly in our heads and we try to show that in our writing but it comes up vague because sometimes, unintentionally, we feel as though our readers can read our minds. Which honestly, I wish was a thing because it’d make writing so much easier.
But the trick to describing stuff is to make it enough to where it’s decently imaginable—not too vague, but not too detail-dumping. Like, we don’t need a play-by-play of what they’re doing or what they look like or what the scene is. In some cases, it becomes boring if we read an action sequence where the writer redundantly said how many hits someone did: “He punched his jaw, then he punched his stomach, and his rib, and his jaw again.” It can also become awkward and choppy, like if there was an intercourse scene, we don’t need to know how many times they grinded or thrusted against each other. Like… we get it.
When describing something, I like to have an imaginary check-list because you need to describe not only the scenery, but the inner thoughts and emotions as well. That, too, can be tricky. But they tend to go hand-in-hand in most scenarios. But on this check-list, I’ll ask myself questions like textures, or what it’s made of, or colors, or designs it may have. And depending on what it is I’m describing, I also think about environments: is it cold? Wet? Dry? Humid? Hot? The smells? The atmosphere? For people, I’ll think about similar things but in regards to how they feel and or think.
So like, in your example, think about the environment first. Where are they? What does it look like? What does it feel like? Then think about what they may be feeling in the moment. Are they scared of this monstrous foe? Are they excited to fight because maybe they haven’t been able to fight something real in a long time? And what about appearances? What does your character look like in terms of her warrior outfit, stance, etc.? What does this monster look like? So on and so forth.
But even with this check-list, it can still be hard to manage and tricky to do, and in that case, it’s always best to read published versions of fight scenes or whatever scene you need help to describe and kind of mimic those. You can also try to mimic movies/shows with how the characters or scenes look as well. The only difference is understanding the emotional/physical part for characters because people do get tired and they do get hurt, so it’s harder to only go off movies and shows because they don’t show how much in pain someone becomes if they get their leg chopped off or when someone stabs them. With that, you do have to do your own research into how other people have written it or if someone can actually describe it to you (which can either be found through writing forums, social media (like if a YouTuber can describe it) or through writing blogs).