Outline exactly and succinctly what the core purpose of the book is. Reveal the purpose in usually fewer than 50 words by describing why the book was written, taking care to accurately get across, not just what the book or document is about, but why it matters. Illustrate how the subject has importance in the real world, and place it in the context of utilitarian usefulness.
Explain the genesis of the work to follow. This is the perfect opportunity to further cement the usefulness of the book by using a personal example of how the topic of the book relates to real life. Discuss any external input that led to the writing, such as focus groups, surveys, or even just being inspired by a movie or song. Take this chance to draw the reader into what made the author or authors excited covering this subject.
Justify the organization of the book or paper by detailing how the book is organized. If the organization is not done in a strictly linear way, give advice on how any users of the book may approach the structure differently. Point out whether any of the sections are optional or tangential to the overall thematic design.
Discuss your sources and their contributions. Explain the use and layout of special features like maps, graphs, sidebars and case studies. If there is an accompanying website or other type of resource that contains further information, mention it and discuss how a reader may access these materials.
Give thanks and acknowledgment to those who provided assistance, inspiration, or help at any point along the way. There are no hard and fast rules for handing out acknowledgment, but the more formal the document that follows the preface, the less inclined you should be to hand out thanks to those who did not concretely contribute to the process. For a less formal book, it is more acceptable to include less conventional acknowledgments.