On the other hand, if you're writing a preface, it's for your own book. A preface, which is included in the front matter of a book, is your chance to speak directly to your readers about why you wrote the book, what it's about, and why it's important. Many books don't require one, especially works of fiction, but if you're wondering how to write a preface, here's an overview.
As it is an introduction to a book, a preface should include information about the book. Consider including a few or all of the following ideas: