Ask Coben how to write a book and he won't hand you a system. His advice runs blunter than that. It comes down to getting words on the page whether you feel like it or not, then fixing them afterward.

The Direct Answer
Just write. You can fix bad pages, but you can't fix pages that don't exist.
He treats writing like a job and warns against waiting for the muse. From his widely shared writing tips.

Bad Pages Beat No Pages

Coben's core advice is almost aggressively simple. The blank page is the enemy, so you fill it and repair it later. He tells writers to shut off the voice of doom that paralyzes them and just get words down, because a bad draft can be edited and an empty one can't. It's the reason he'd rather produce a rough page than protect a perfect idea.

You can always fix bad pages. You can't fix no pages.

Harlan Coben

Write Like There's a Knife at Your Throat

His second theme is urgency. Coben tells writers to make every word earn its place, and he points to Elmore Leonard's rule about leaving out the parts readers tend to skip. He also rejects waiting for inspiration, comparing a writer to a plumber who doesn't sit around waiting for the muse before fixing your pipes. And he swats away the time excuse: skip the TV show, wake an hour earlier, write on your lunch break.

He backs it with a numbers argument. Writing, he says, is one of the few activities where quantity turns into quality, because the more you write the better you get at it.

His habits put the advice into practice. See the full Harlan Coben writing routine for the daily grind behind it.

What You Can Steal