Read great writing and learn from it. Learn the craft. For thrillers, read the first chapter of Lee Child’s “Persuader.” You’ll want to read on, but that first chapter shows everything a thriller should be, and how it’s different from a conventional mystery. Most of my work is modern noir, although “Deadline Man” was a thriller. I advise all writers to read Julia Cameron’s “The Artist’s Way” and do the exercises. Beyond this, write. When I am really rolling, I do a thousand words a day.