Ok, so I set myself a goal: To write a historical fiction novel this year. My subject will be Agesilaus (400-360 BC), the Spartan King whose reign is often viewed as the beginning of the downfall of the greatness of Sparta (he ruled about 80 years after Leonidas). But instead of doing what I normally do, and just jumping in and writing furiously (which usually nets me four chapters at most), I am going to prepare first.
I'm starting with reading a couple of other novels set in the same general period. Meanwhile, I am also reading up on the actual scholarly history of the period, and as much about Agesilaus as possible in particular. THEN I am going to outline his story in as much detail as possible. And only after that is finished am I going to actually start writing.
At least, that's the plan.
I already have some ideas for specific scenes in his life, and I will probably outline each major character in detail. That's where my experience as an RPGer comes in handy. I'll treat each major character as if he/she were an RPG character, and detail them accordingly.
And there we go. As of yesterday, I am off and running. Having just finished a bit of fantasy fiction, I am now reading the first period novel, Gates of Fire by Steven Pressfield. It's about the battle of Thermopylae, and is considered the best book on the subject.
Special thanks to Scott Oden for pointing me in the right direction, and for his indispensable advice.