Part one
Writing a book is not one big act of inspiration. It is a few hundred small, repeatable decisions made in order.
Write your story as one sentence: a character wants something, and something stands in the way. If you can't finish that sentence, you have a mood, not a novel yet.
Then ask the hard question: can this idea survive forty scenes? If it can't, widen the stakes now.
You don't need a full outline, but you need a destination. Knowing the last image of the book keeps the middle from wandering.
Twenty to thirty one-line beats — “she finds the letter”, “he lies to his brother” — is enough scaffolding. Chapters are a formatting decision you make later.
500 words a day finishes an 80,000-word draft in about six months. 1,000 halves it. Choose the number you can hit on a bad day, not a good one.
Do not edit chapter one while drafting chapter nine. Leave a bracketed note — [fix her job here] — and keep moving. Momentum is the only thing that finishes books.
Put the finished draft away for four to six weeks. You are reading for structure next, and you can't see structure while the sentences are still warm.
Pass one: structure. Cut, reorder, or add whole scenes. Pass two: scenes. Does each one change something? Pass three: sentences. Only now do you polish.
Then send it to three readers who read your genre and won't be polite.