Outline. Outline, outline, outline. When I started writing more than thirty years ago, I jumped into each new idea and cranked out a couple of chapters...sometimes only one. But once the fire in my gut had burned out, I had nothing to keep the story flowing. The outline, something as simple as ten bullet points, diagraming the story from start to finish, allowed me to "first draft" a complete novel and then flesh it out with detail on second pass. I've completed more novels in the last two years than the prior twenty years combined. Outline. Even if it changes before you get to the end of the first chapter, it will hold your hand getting you to the end.