Sheila goes into visualizing the novel while writing.. This is so much the process that I follow, that rather than rewrite it, I’ll just say, “What she said.”
(Except to note that, as I am a complete pop-culture non-starter, I don’t cast these things with actors. I never know who those guys are, except for the mega-names, whom I generally detest. And Phillip Seymour Hoffman. I adore Phillip Seymour Hoffman. No. I cast people who are loitering in my head reading books, smoking cigarettes, and saying rude things to passersby. If they’re going to be cluttering up the space, they might as well become employees.)
If you don’t know how to visualize, here’s a workshop that can get you started.
Also, Sheila is utterly correct in her comments on advances. If you advance stays within range of your sell-through, you’ll stay employed. A number of very good writers have received sky-high advances early on, only to have a less-than-stellar sell-through annihilate their careers.