Wrote my first "novel" when I was six. Studied a bit in college, but then pursued history... But when I started writing professionally, it was mostly learn as you go.
Before writing, I start with a series of questions, specific things I need to know before I can write the book... That list grows and changes as I do more and more research. But when I've answered the bulk of the questions, I begin to write...
As I write, invariably I encounter more questions and answer those as I go.
I write every day for most of the work day, and I try to write 2,500 words per day... If I don't make it a routine and treat it like a job, I'd never get anything done.
Writing about craft has forced me to think more about my own writing technique, and to break down my process in ways that have been enormously helpful to me.
In teaching writing, I'm learning new things about writing.