How to summarize the book after completing a book, and reference of books?

After finishing to write a book, it is very essential to revise it by a thorough reading with a special focus on text, grammar, spellings, punctuations and to correct the errors. Sometimes it is not enough to read it once and you need to read it several times until your satisfaction.

I don't think that there is a need to summarise your book because a book is more understandable with more elaboration.

Yes, you need to annex a preface in the start of a book which contains important information about a book. It is preferred to write it after you finish your book.