You have an idea that you believe would make an excellent book, but how do go about selling your idea? Can you just send your manuscript to a selected publisher? Probably not. If you do, it will probably hit the trash can before it is even opened. Follow these steps to give your book the best chances of being published.
Search for a publisher who might be interested in your style of book. Most publishers are very specific about the types of books they publish, and will only consider books that will fit their mold. There are also many publishers who only work through agents or with previously published authors. One way to search is by using the Writer's Market.
Pick out three or four publishers who appear to be interested in your type of book. Thoroughly research them by perusing through several of their published books. If possible, go to their websites. Email or write them for a copy of their writer's guidelines. In the guidelines, it will state exactly how to submit a book idea to them and whether you can do it online or have to do it through the mail.
Write a one page query letter about your book. Depending on the publisher, you may to able to send them an email attachment or they may require a paper letter. If possible, address your letter to the person who makes the decisions. This query letter is your sales pitch. Without exaggerating, make your book seem as exciting as possible. In your query letter, give your book a title.
Wait for a response to your query. If the publisher invites you to do so, write a book proposal. Find sample book proposals online or use the Writer's Market for examples. Include in your proposal why you believe your book will sell, a market analysis of the current book market in relationship to your book, an outline of the chapters of your book, a projected date when you'd be able to complete the book and two or three sample chapters. Of course, follow the writer's guidelines sent by the publisher and make sure to include everything they ask for.
Wait for a reply. This is probably the hardest part. If they like your proposal, they will negotiate with you to determine when you will be able to present them with the entire book, when they can publish it and how you will be paid.
Stick to one page for your query letter. Publishers get hundreds of queries a year and they want to be able to look through them as quickly as possible. If it is more than one page, it may hit the trash can. If your selected publisher wants a query letter by mail, make sure to enclose a SASE (self-addressed stamped envelope). Without it, you may never get a reply back. It is OK to submit query letters to more than one publisher at a time; you don't know who might say "yes."
Do not expect to sell your book instantly with your first query letter. Some writers work years before being invited to write a proposal or actually having a book published. Be patient.