I have recently been keeping a Story Bible for my novel-in-progress; Outlandish (you can check that out on my projects page).
One might ask, "What exactly is a Story Bible, and how do I use it?"
Well, I'm here to answer all your questions.
A story Bible can be handwritten or typed. The story bible is where you can keep your character descriptions, and worldly aspects. This is a helpful tool when writing. You can reference this when you need to know something as simple as a character's hair color, or you need something as extreme as the way they would respond to certain situation.
I got this idea from a YouTube video, which you can watch here.