I write like a painting. I start with an outline, and then I fill in a wash of the vague action, usually in parentheses with bits of dialogue that I already know. So that the first version looks kinda like:

(Anora and Alistair have a vaguely human conversation)
(until sex comes up)
(Alistair makes it worse) "Do we... I mean, did you have a specific quantity in mind, or something?"
Anora (sits in stunned silence). "No," she managed, after a while. "I don't have a sex quota."
(Anora gets offended, tells him he smells, they part, teh awkward)

And then I fill in the actual words and details in whatever order they come to me.

And... then I send it to my lovely beta, who rips it to shreds and usually makes me rewrite the whole thing. Like, you shoulda seen the first version of Dark Overture. I think literally the only words the first draft shared with the final were "Your light shines in the dark."