The preface is written by the author and addressed to the readers directly. It is more often found in non-fiction books. 

You could tell the readers why you wrote the book. Does it fill a need? Were you inspired by a particular incident? What is the purpose of this book?  

You could also talk about the writing process. Why did you decide to turn your blog into a book? What were the challenges you overcame? How did you change or what did you learn in the process of writing this book? How did you research it? How long did it take you to write this book?

Yet another aspect you could write about is reader assistance. What will the reader gain by reading it? Should it be read in a specific manner?

Finally, you could summarize the material contained in the book. What are the major themes? What are the steps to the final goal? What are the highlights of each chapter?

Choose one of these viewpoints in order to keep the preface short, less than two pages is ideal. 

This section is also paginated with lowercase Roman numerals as part of the front matter. If there are two prefaces, one written by the author and the other by the editor, the editor’s preface comes first.  If there is both a preface and a foreword, the foreword is first. 

Assignment: Decide which aspect you would like to discuss in your preface.