Spend a few minutes thinking about this rather obvious question. It will help you establish priorities. For example, do you want your book to be published because you have a burning desire to write, and your career as a writer depends on being published, or do you intend it to support other activities such as lecturing or training or your general professional development; a book gives credibility to your wider profile?
Looking in the current Writers' & Artists' Yearbook is a good place to find a publisher that covers the kind of book you have in mind for your first book, and remember that you don’t have to actually write the book until you secure a contract with a publisher. What you will need is a synopsis, an approximate word count, and number of photographs/illustrations that will support the text. Many publishers welcome new manuscripts, so get on contact with them, and get the name of the commissioning editor in order to approach him/her directly with your idea. You may be asked to submit the first two or three chapters.
Next: The Publishing Process