hellaoo uhm I wish I could give a more constructive answer but I have no background in literature and I truly only write from vibes, so idk if I'm even qualified to answer this😭 but the short answer would be that I've been writing for over a decade now, and it honestly depends on the story I want to tell.

The long answer is life experiences, ample exposure to other people's life experiences (bcs of my job/jobs), a clear cut picture of how I want a scene to look like in my head 24/7. Most of my fics came to fruition bcs there was/had been a particular feeling or scene bugging me for weeks in the form of vivid imagery. Sometimes it's just the image of a character slumped sideways on the sofa in the dark while the TV reflects off of their wet cheeks. I mostly write abt images that haunt me (aside from smut bcs that's a diff conversation). I didn't have a solid writing style or one distinct enough to call my own until I hit 20 or sumn bcs my writing had always been chaotic and I had also been overly critical. But as I grew so did the horizons of my imagination and I like to imagine I'm not writing for anyone but for the void. Like when I publish a fic, it's not for me or anyone in particular but for the void to accept and call its own i.e. it is no longer mine. That way it's easier to not feel so tied to a piece of work to the point of emotional anguish (I do this for academic literature too).
I also read less when I'm writing bcs that helps me personally to focus on the characters in MY head and not anyone else's.

Also thanks to the nature of my work, I pick up on mannerisms and micro behaviours. That all adds to the compelling narrative. It doesn't have to come up a lot, and it doesn't have to be a central focus of a particular scene but more in the sense that "it exists bcs it cannot bear to not exist". This way the plot outline doesn't look like a looming feeling for the reader (imo) bcs focus too much on details you throw off the balance, and focus too much on the main plotline, your readers will feel like they're being chased by the narrative instead.

Also dialogue. I think I'm someone who builds a lot of scenes around dialogue, but hate when the dialogue crowds it instead. So with dialogue I always edit with the intention of removing any unnecessary parts, rephrasing things to shorten it, and reading it out loud a few times to make sure it sounds natural aloud bcs a lot of times we assume that just bcs it's written, it will work. But the truth is that we still read it with our internal voices, and if it sounds like a mouthful when spoken irl, it is still a 'mouthful to read' (ofc not including climax/pivotal scene dialogues bcs those cannot truly ever be too short).

In conclusion, I love repetition I love haunting details I love circling back to seemingly unsuspecting details I love italics and em dashes I love torturing my characters I love when characters are so human they forget to be characters and say the compelling things they should supposedly be saying and I love writing the complexities of 'being' and the general weight of it all.

This is way way way too long but thank you for tuning into the Kiki Radio a.k.a Yappatron3000💗