Next create a preliminary outline before you begin the actual writing of your book. This may change as the writing progresses, but you need a guideline to start with. Your outline should be built around your chapter titles. Perhaps you have 10, 12, or more.
Then write a paragraph about each chapter. Be aware that this may change drastically, but it is important to get down as much information as you can.
Each point must support the main theme. Each chapter, though self-contained, needs to promote the main idea of your book.
Example from Wounded by Words:
Chapter 1: Hurtful Words – Caustic words and demeaning statements can be as dangerous to our wellbeing as any weapon. People often use words that dominate and control when they feel insecure themselves. Unfortunately these words are often directed at close family members, often children, and the outcome is much pain and suffering. The tension resulting from these heated words often leads to the telling of lies by both parties.
This concludes Step 1 of the Three-Step Writing Process. Lay your work aside before continuing.