An author who wishes to publish his or her own photographic book is well advised to begin by investigating publishers and their requirements. There is little point in preparing material for a book that someone else has just written and published, or submitting material to publishers who do not publish photographic books. It sounds obvious, but all publishers still receive work that is entirely inappropriate for their lists.
One of the best places to begin an investigation of publishers' requirements is a book shop. Browse the titles available from particular publishers, and note those that are most like the book you have in mind. Publishers' websites may also provide useful guidance on the types of books they consider for publication. A third source of valuable information is obtainable through one of the trade reference works published annually for prospective authors, although some of these have ceased publication in traditional form and moved on to dedicated websites.
Remember that standards are usually very high. A publisher looking for a book on travel photography, for example, may consider quite a few submissions before awarding a contract to a particular author. However all the submissions, including those that are rejected, probably incorporate excellent written and photographic work. The submission of the chosen author may have had broader scope, greater depth, well-considered supporting text etc.
Photographic books of the "how to" type are often of more interest to publishers than "coffee table" books. Have a look at your own shelf of photographic publications and note what types of book are included. Other photographers accumulate broadly similar collections, so publishers may be striving to produce the sorts of books that are on your own bookshelf!
Always obtain independent advice from those with relevant experience. It is all too easy to convince yourself that your images are fantastic and that a publisher will want to use them. Unfortunately, others may see things differently and perhaps feel that the quality of the work is not sufficient to attract the huge investment required to publish a new book. Another consideration is whether you feel able to write the text for a photographic book. A "how to" book might be supported by 30,000 - 50,000 words, and many publishers say that the words are more difficult to get right than the photographs. A submission may therefore be turned down, despite excellent images, because too much work is required to achieve the required standard for the text.