Sometimes finding a title for your book is more difficult than writing it; other times you have a title without the story. It never hurts to write down title ideas for use later. Having a “working title” is common, so don’t worry if you don’t have one until you’re ready to publish.
Usually at some point your muse will help you out with a title, which may come out of the blue when you’re in the grocery store or just starting to fall asleep. Other times you have to work at it. If that’s the case, start with keywords related to your story, its theme, or message. If it’s character-centered, focus on who or what your protagonist represents.