Check to see if anyone else has written a book about a branch of your family. Ask your local librarians if they know where you can locate one of the many catalogs that include lists of published family histories. It may save you time and give you information you haven't seen before. When you have finished writing your story, have someone read it over for grammatical and typographical errors. Typos that change Jan into Jane or Tate into Tote will drive everyone crazy years from now.
Family books make wonderful gifts at reunions or holiday time.
No matter how small your book is, relatives will be pleased to receive it. Don't assume that no one else is interested in your family besides your family. In fact, you should even write the Library of Congress and suggest you send them one to add to their collection of compiled genealogies. Write to the Library of Congress, Genealogy Division, Washington, DC 20540. Your future will thank you.