In teaching writing, I'm learning new things about writing.
Guy Kay is probably my favorite and the writer I most want to emulate.
The closer you can get to your setting and to primary sources, the more authentic your history is going to be.
As I write, invariably I encounter more questions and answer those as I go.
Guy Gavriel Kays Tigana is, in my opinion, one of the best, if not the best fantasy novel ever written. Its beautifully written, the characters are unforgettable, the worldbuilding is exquisite.
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.