For Alice I had a humongous banner-paper timeline of EVERYTHING. Every trans media. Every character. Every book. And I strung them together.
But really, each character was just a certain aspect of my personality. Cara was my snark. Alice was my nerd. Andrew was my "why do I keep liking this kind of guy"
Now, I'll sketch out in a little journal who my characters are, what they want/need, etc. but I find it more freeing to just get going. I know these people. They're me, they're my friends. They're them. Whatever they do is 'right' for them.