Step 2 of my Three-Step Writing Process is writing the First Rough Draft. To write your first rough draft, you use the creative (right) side of your brain.
Find a large block of uninterrupted time and write all the information you can think of regarding your book. Don’t get hung up in grammar, punctuation, or phraseology. Write whatever comes to mind. Some of your chapters will be briefly outlined on this first rough draft, others may be in detail, and some won’t exist at all.
You may choose to write a synopsis of the entire book, or you may want to take smaller chunks of your “elephant” so you don’t get indigestion. On the first sitting, I write a brief overview of the book. After that, I usually write a chapter at a time, so I’m usually dealing with 15-20 pages at a time. I follow the same steps for each chapter. If there are personal stories within the chapter, I use the same process for each story.