Skip to Step 2 if you have a literary agent. Otherwise, submit a query letter to the publisher, John Wiley and Sons. Wiley does not accept unsolicited manuscripts or book proposals, but does accept credentials and contact info. Write a professional business letter that includes a brief description of your idea and why you are the right author for the book, detailing your areas of expertise and any professional writing experience you have. If you don't have any, don't mention it. Send your letter to:
Susan Spilka, Editor
John Wiley & Sons, Inc.
111 River Street
Hoboken, NJ 07030-5774
Prepare a book proposal. If you have an agent, you can skip Step 1 and have your agent submit the proposal for you. Otherwise, wait until you are contacted by the publisher and asked to submit a proposal, so that you don't do all that work for nothing. Your proposal should include a cover letter, an overview of the planned book, a table of contents, a chapter-by-chapter outline, two sample chapters, a profile detailing your professional background and any clips that might help sell you as an author, such as articles you've written or professional reviews of your work. Also include a postage-paid return envelope if you would like the publisher to return your proposal when finished with it. Study other "For Dummies" books to familiarize yourself with the format and style and craft chapter headings that demonstrate your familiarity.
Write the book. Upon acceptance of your proposal, the publisher will provide you with detailed guidelines to help you format your manuscript according to their standards. At this point you'll have done most of the background work, so writing the book is just a matter of fleshing out the chapter-by-chapter outline included in your proposal.