One method, according to author Silvia Hartmann, is the A-Z model. The point is to sit down and brainstorm a list of topics you find interesting. They don't even have to be related; just start thinking. After this, fill in everything you know about the topic. After you get a few specific topics you generally know a lot about, write a short paragraph on each. Then choose which flows best and which you feel most comfortable writing about. This method tends to work very well for shorter books as well as e-books.
One writing style tip, designed by award-winning author Dr. Randy Ingermanson, is known as the "Snowflake Method." Ingermanson claims that the design process of a novel (or other applicable work) involves starting small with an outline or "skeleton" of a story. He visually likens the initial process to the shape of a triangle. As the process continues, the writer adds more and more detail to the basic story until a full story emerges. In the meantime, the "visual" goes from a triangle, to a star, to a snowflake. (See references for a link that will show you a diagram of this method.)
One of the most common writing tips offered to any potential author is free writing. This technique allows you to sit down and just write. You write whatever comes to mind, giving you the opportunity to open up and flow. This method tends to give birth to new ideas as well as staving off writers block. Your ideas don't have to flow in a specific order, just write whatever comes to mind. The purpose of this method is to get your pencil (or keypad) moving, so don't over-think it.
If you find yourself stuck before you start or you keep running into mini road blocks, take a break and remember not to take your writing too seriously. Just do your best and remember it's supposed to be an enjoyable process. Keep the book contained, don't try to write the whole thing at once, but write one chapter or section at a time. This will help keep the creative juices flowing. DO NOT re-read what is written. Continuously move forward. If you keep reading what you already have, you'll want to endlessly edit and change the story, keeping you stuck in one place. Also, attempt to spend at least 15 minutes a day on your book. If you don't work on it every day, you'll eventually put it to the side, and it will become less of an ambition. Don't forget to enjoy yourself and let your creative juices flow.