I'm in the midst of this process, now, so no spoilers.
- Think of possible titles that you like, that speak to your tone, style, subject matter, and potential audience.
- Google them.
- Cross off all the ones that are already taken, especially in book titles, but even in movie titles.
- Take your top available choices, and mull the over.
- Run the titles by friends and acquaintances, to see what they think. What would they think that titled book is about? Would it pique their interest? Does it seem appropriate?
- Make your final decision.
- Be willing to throw that one out at some future point, and re-title it, anyway.