I'm working on my third novel, my fifteenth book, and I'm approaching it as many writers do: from nowhere! It's an exploratory process, and I don't really know what the book will be about. I have a good idea, a handful of characters I already love (and hate), and a kind of plot. But I do have my storyboard, and that's gotten me a lot further along than I would be without it.
You've probably heard of the plotter versus pantser continuum in writing. Plotters like to know where they are going, in every degree, before they begin. Pantsers are the opposite--they feel their way along, following the nudges and ideas that come as they generate writing. I fall somewhere in the middle. I don't think I would've gotten thirteen books published, fourteen written, without some planning. But I also know I gained a tremendous amount by letting the muse direct some of my steps as I went forward.