How to begin a book?

I'm often asked "How do I begin a book?" or "When I start a new story, I feel really inspired, but somewhere along the way I lose inspiration or the story fizzles--what do I do?"
Getting past chapter three is a challenge for many people, including me. To keep going without getting permanently derailed, I always remind myself that IT'S OKAY TO WRITE BADLY. During a first draft, we're not trying for deathless prose; we're just trying to stay alive. When it comes to the first draft, perfectio...