Compose a clear and enticing query letter with which to contact a literary agent. The agent will then help develop a book proposal and, when complete, submit your proposal to commercial publishing houses. You are more likely to meet with success if you work through an agent, but you can also submit your book proposal directly to publishing houses. Think about the essential idea of the book and craft a one to two page query letter which explains this idea concisely, yet effectively. The query letter should also contain biographical information which explains your expertise on the subject and why you are the best person to write this book.
In order to find agents to send the query letter to, research which agents have handled books about the subject matter reflected in your idea. Do so by looking for authors' attributions to their agents in the preface or acknowledgment sections of their books. Consult the "Literary Marketplace" (available at libraries and bookstores) for a roster of agent names, alongside their specialties. After narrowing down your list to 10 names, send the proposal out to each and await a response. If no one responds positively, send your query letter out again to another 10 names.
Write a book proposal after an agent responds positively. Your book proposal should consist of an outline of the entire book, which means you must conceptualize the entire manuscript from initial idea to finished product. Spend time thinking through how you want to develop your idea into a book-length manuscript (approximately 150 to 200 double-spaced pages long).
Go to your local bookstore and library and scan the shelves in the section in which you envision your book, since your proposal must also contain a summary of the market in which your book will compete. If other authors have written on similar subjects, note their names and book titles. If no one has written on your topic, take note of this as well. Condense your findings into a brief report in which you detail what you saw, again reiterating why your book will add to the field and provide necessary information.
Write a sample chapter. Particularly if you are an unpublished author, an editor will want to verify that you can write capably and have enough to say about your subject. Write a chapter for your book that is approximately 30 to 50 pages long and can serve as an example of writing that is clear, stylish, informative, and engaging.
Scan library and bookstore shelves to see if you can find a publisher or several publishers that are likely to be receptive to your idea. Submit these names to your agent, or if you are contacting houses directly, research address and editor names so that you can send your complete proposal in when it is ready. This can be a long process, so prepare to be patient. Your agent will manage sequentially submitting your proposal to different editors and let you know each response.
Work with your editor to bring the entire manuscript to fruition. You may write the entire manuscript and then submit it for a rewrite, or submit in sections or chapters, responding to your editor's feedback. Once text is approved, the book designer and production manager will oversee jacket design and production scheduling. In about 6 months to a year after you complete your manuscript, you will at last hold your published book in your hands.