I play a character who is a little like Thomas Jefferson at Colonial Williamsburg and practically I practice a kind of "outside-in" acting where I inhabit the character and half-ass it if I must [1] and then feed back my experience towards preparing to do better next time.

I am in the middle of writing my own version of a "legendary" story where over the course of centuries years of retelling a fireteam of 3 men becomes an army of 80,000, fictional sources don't agree on who exactly was involved, people who speculate about real life people the story might be based on left an obvious suspect out, etc. I am in the middle of writing up a rather long document which tells the story in such a way that I can memorize the names, the dates, the places and be absolutely confident about the details -- and of course I have to be able to speak authoritatively about the historical period and explain what people believed, why they did what they did, etc.

At the moment the story is getting harder to tell but I'm practicing at starting with the most bombastic story first and working towards a historical explanation but it is worth it because it's a personally meaningful story which is the centerpiece of a backgrounder for my character.

My wife says "don't tell the story to people until you get it right" and I just blow that off because I've been telling this story for a while and doing all the work because I want to do it better. And it's going to be the foundation of how I do all the writing for this character.

[1] e.g. rule one is to break character before I get seriously flustered and talk about my immediate experience