Often times, the easiest way to structure a book is to start at the beginning and move forward through time. Structuring your book chronologically is not only a natural storytelling technique, it will also give you an easy starting point, and knowing where to begin your story can often be one of the largest hurdles of telling it.
If you are compiling your family history, for example, you may want to make your first chapter be about your earliest ancestors (or however far back you can trace your family). From there, you can use one chapter for each generation of the family (grandparents, kids, grandkids, great-grandkids, etc.). As an added bonus, this also gives your contributors an idea of where to add their own content.