Make a list of subject matters in which you have expertise. Be specific. For example, if you're an expert on ancient Greece, write that down instead of just "Greece" or "ancient history." Most titles in the "For Dummies" series are fairly specific, so you'll want your subject matter to be very focused as well.
Visit dummies.com to see which "For Dummies" titles are in print. You don't want to spend weeks researching material for your book if the company already has the same or similar title in print. Choose a title to work on that Wiley hasn't published yet but for which you see a market.
Read as many "For Dummies" books as you can to get a feel for the format, style and tone of the series.
Write a book proposal. In general, nonfiction authors sell proposals, not books. A proposal is a 15- to 30-page outline and pitch for your book. The proposal should include an overview or outline of your book, a section on marketing and promotion (for instance, whether you plan to do readings or workshops based on the book), a list of competing titles on the market and how your book differs from them. Include a brief author biography, as well as a table of contents, summary of each chapter and two to three sample chapters.
Write a query letter---a one-page summary of your book---to send to literary agents. Find agents who represent nonfiction writers by buying and reading the most recent edition of "Guide to Literary Agents," a comprehensive directory of book agents and the genres they represent.
Mail your query letter to agents. Don't send an unsolicited book proposal to an agent unless her guidelines specify to do so. If an agent is interested in reading your proposal, she will write or call you. Some agents accept query letters by email. Always read each agent's guidelines carefully before submitting your query letter.
Wait for a response. After you've signed an agreement with a literary agent, it may take several weeks for her to receive a reply from a Wiley acquisitions editor. If the company is interested in publishing your book, your agent will receive a contract on your behalf, and she will negotiate its terms for you, including royalties and deadlines.