Before embarking on a new book, I think it's important to let the idea stew and "marinate" in your mind for a while. One of my favorite writing books is Orson Scott Card's "How to Write Science Fiction and Fantasy" (I'll provide a link for you...I don't profit if you buy it, so buy one of my books while you're over on Amazon.)
Card suggests, in an upbeat, positive way, that you don't have to wait a year before writing that new novel, but you just might be ready to dive into the one you were thinking about LAST year. Writers always have lots of books bouncing around in their brains, so it's great to let them simmer for a while before letting their savory juices spill out onto the page. (Boy, I gotta get a sandwich!)
For me, I find that my ideas kind of fizzle out if I don't fully embrace the concept. That means spending time doing some research, drawing pictures, sketching out ideas, outlining a plot, writing up character concepts, and generally playing make-believe with the ideas. Staring off into space, thinking about what fun things could happen with my characters is part of the excitement of the writing process and is an important step toward getting the book completed.
If you spend time "being" your characters, and you spend time wandering around your imaginary world, the book often writes itself from that point on! A tip from me: be sure you don't let the planning and marinating phase become permanent! Lots of great ideas happen while you're writing. I've had characters' dialogue and changes in the plot happen just while I'm writing. It's the most exciting feeling and it comes from really understanding your world and the people you've placed in it.
Marinate on that.