Hi, JawJaw, so, I see you got an early start! Sorry you've been waiting around for an answer. Anyway, that's a good question: How to get started!
First, I'd suggest, you discover the story you MOST want to tell. A memoir isn't writing about a whole life; it's writing about a slice of a life. So which thread of your life do you most want to explore? For example, in my first memoir, I followed the theme of what it was like growing up in my incestuous family.
In my second memoir, I followed the theme of recovering from sexual addiction.
A memoir can be about any aspect of one's life: what was it like growing up on a farm in Kansas? What was it like growing up in a military family that moved every few years? What was it like to suffer from a serious illness? What was your journey through a divorce?
If you're not sure which aspect of your life holds the most interest for you, then try freewriting about several aspects and see where your energy leads you.
In short, though, every memoir, for the most part, follows a thread or theme. That way, you won't be taking on too much information--more than can comfortably be contained in one book.
Does this make sense?
In other words, which aspect of your life is the one that feels as if you must write it NOW!