Your subject will find you.
At least that's the theory. You're supposed to be open to it. Let it insinuate itself into your life, hunt you down, insist upon being written. Unless of course you're the sort of crass commercial writer who wakes up one morning and thinks, 'Vampires! They're popular.' And then an hour later, 'Pirates! They're popular.' And then an hour later goes off and writes Vampirates. And an hour later finishes it.
To be perfectly honest, I'm starting to think that ole Vampirates guy is one smart cookie. He's on Book 8, while (two years later) I'm still wrestling with life, death, mortality, God, love, families, weather and a small penguin crossed with an anteater (why?). Yes, I know I said it was finished. What I meant by 'finished' was 'not finished'. Today I decided what it really needs is another year.
In my head, hatching like an adorable, unattainable little egg, is the next book. The next book is going to be simple. Linear. Two characters, maximum. Not much will happen. It'll end happily and uncontroversially. No Gods, no penguins, no floods. The next book is going to be the literary equivalent of Forrest Gump.
You got that, Subjects (all of you)? From now on, you don't choose me. I choose you. One at a bloody time.