1. Before you begin to research and write, take time to write notes to yourself and answer these questions just as a journalist would ask: Who, What, Where, When & Why. Who and/or What is your book subject; Where does it take place; What is the timeframe; What is your theme; Who will be interested in reading your book and Why is your book relevant/current. The “Why” is also why you are writing your book. 
2.  Draft a concise Introduction. That will help you to know more about what to research and give you a loose structure of your book. It can also be the beginning of an outline if you like. The meat of the Introduction comes from the notes that you write to yourself in Quick Tip #1. A good Introduction establishes the tone of your book.
3. Determine some basics: When and Where will you do your writing? How many hours a week will you spend writing? What tools do you need (note pads, pens/pencils, computer, etc.)? Will you write on note pads first or write straight into a desktop publishing app on a computer? (MS Word is easily converted to pdf for publishing.) 
4. Just start writing. There are many moving parts to getting a book published but for now, just start writing. 

BONUS TIP: Don’t be concerned with editing, formatting, book type (hardcover/softcover/eBook) or anything other than the writing. 

YOU are the Boss, the Writer, the Author! Good Luck and Have Fun with the writing!