i need to stop playing

Since everybody and their momma's momma are writing a book, I need to stop playing. What am I waiting for? Some mysterious talent to hit me? Um, I'd be waiting all day if I am waiting on that. I mean I could probably write a decent book and get a decent advance for it. I mean honestly the advance is all I want (got my eyes on the prize). I'm not going to do fiction, just yet, I'll stick to nonfiction. So what I need to do is conceptualize an idea, do a proposal, find an agent, tweak said proposal/idea, submit to publishers, get a an offer, receive an advance check, write book, and market book. Sounds like a plan.

Step one: what to write about?