- Learn about the era. Who was the emperor? Why has my protagonist been sent to the outermost point of the realm?
- What actual events can I weave into the story that will give it more substance?
- How did they dress?
- Transportation - especially for women. Did they have carriages?
- How advanced were the local people?
- What were the local's disputes?
- What were the names of the weapons of the era?
All of this needs to be learned before I can start developing the characters. Full backgrounds need to be worked out for each of the main characters before I can start writing the first word. If I don't know the details of my character's lives before the book starts, then there is absolutely no way I can write a meaningful and gripping story about them.
In my opinion, pre-writing and research is as important as writing the story, and possibly more important than editing.