How can I minimise the "filler" text that I end up writing when fleshing out a scene with detail?
An appropriate level of detail seems to me to be a fundamental requirement for good prose. Whatever I may be trying to achieve in terms of characters, plot, etc., in the here-and-now of each paragraph, each sentence even, telling a story is not the same as writing an outline. There needs to be enough detail to make the story feel real.
However, I find myself agonising over the seeming randomness of the information that I add to a sentence, paragraph or scene, in order to flesh out the world of the story and make it convincingly real.
A working example... A Main Character walks into a shop, and by coincidence encounters some other important character; character development happens, plot happens, motivations and values are explored, painful choices are made, all that is great. But it will often feel wrong to just have two "talking heads". Rather, the story feels real when the shop is described, as well as the products, the other customers; the owner interacts with some of those other customers; we get an overview of the space, and a few telling details too; and the main character's actions are related to this environment, for instance she goes and sits down on that couch we just described, or looks into that mirror--while what is actually important is the conversation she is having.
But why is the couch brown? Or green? Or why is there a couch there at all? Why is the mirror on the wall, or on a stand? Why was the other customer an old lady with a large handbag--or a teenager, or...
I have three possible answers to my own question (given next, in increasing order of sophistication [obsessiveness?]), but they don't feel enough.
Answer 1: "just do it". Stop obsessing and make up some details, so as to make the story feel real. It doesn't matter what they are, so don't worry about it. And, in any case, your intuition should make the details interesting--just let yourself follow the theme, or atmosphere, of the story, and make up details that seem to fit. But stop obsessing. (Did I say stop obsessing?)
Answer 2: the details don't matter in terms of the sort of "content" that you might put in an outline, but there are other qualities that make prose good, which you cannot plan for. Prose has rhythm, and a "music" to it, and is infused with attitude, emotion, atmosphere. It can "show" a PoV character's frame of mind though its organisation. Not to mention that it can do worldbuilding, one tiny detail at a time. So whether the couch is brown or green may depend on whether the sound "brown" or "green", irrespective of the actual colours, fits in with the sound of that sentence. The metaphor used to describe the mirror may indicate how the PoV character is feeling, e.g. introspective, or full of self-loathing, or narcissistic--so start with the metaphor, and it does not matter what the mirror has to look like for the metaphor to actually describe it.
Answer 3: one of my favourite "principles" is that "every component of a story should have multiple functions". Basic example of the principle: we don't write an "action scene" with nothing but action in it, then a "character development scene" with no action and only dialogue or thoughts in it, then a "plot advancement scene", then an "emotion scene", etc.; rather [it is almost always better if] every scene does all of these things. Well, apply this principle to the "details" as well: every word can foreshadow something, or do a little worldbuilding, or be described in a way that reflects how the PoV character is feeling. So make a list of important ideas that are not the main purpose of the current scene, and draw on them to flesh out the details of this scene. E.g., put in a couch that somebody will trip over later during an action-heavy scene; or use a fabric for it that is in short supply due to something important in the backstory; or make it as black as the PoV character's despair.
But this couch, which will be tripped over, which is made of a fabric that is in scarce supply, and whose colour reflects the protagonists' mood... Why is it on the left side of the shop? Why are the cushions round? Why is it a three-seater?
Indeed, at some point, maybe it's just bad to try and make every single word meaningful in some way... But if so... Why green and not purple?
Edit: re-reading my question as posted, it seems to focus too much on the sentence-level details, but that's just because of the examples I picked. My question applies more broadly. For example, say I have a scene in a forest. There will be a chance encounter between two characters. They will have competing objectives, and there will be an unfair power dynamic between them. There will be values explored and choices made etc etc etc. But is the forest on the side of a mountain? What specific trees and other plants are there? And it's not just about describing the scene. How do the characters meet? Does one surprise the other? Or does the PoV character hear the other from a mile away? Does she try to hide, then change her mind and show herself? The actions leading up to the meeting may be necessary for the chance meeting to feel real, but if I actually only really care about what happens after the meeting, they may be "randomly choosable details", too.