For now, very helpful tips can be found at Tenured Radical. The advice is directed especially toward those with a dissertation being revised into a first book, but much of it applies to, e.g., law professors writing a first book after years of article writing. Be sure to read through the comments for more.
Sivacracy, which gets the hat tip, follows up.
Al Brophy had a post on PropertyProf a while ago with thoughts about selecting a press.
Many editors and agents recommend Susan Rabiner and Alfred Fortunato, Thinking Like Your Editor: How to Write Great Serious Nonfiction--and Get It Published. It is directed especially toward academics who hope to write for a trade audience, but much information is relevant for those writing with an academic press in mind as well. E.g., what goes in a book proposal? How do you think about the "audience" question? The book is especially good at helping you to see the way marketing concerns (which every press will have) affect the way an editor will view your proposal. The sample proposal in the book is a trade proposal. Academic press proposals would spend more time stressing the book's contribution to the existing literature, the importance of the arguments, innovation in the research, etc.
Whether you are a law professor moving from articles to books, or a recent Ph.D., if seeking a first book contract, you are an unknown in the book world. In your first contacts with an editor and in your proposal, pitch yourself as well as your project.
This will sound hokey, but you only have one chance to make a first impression. Don't hold your work back too long, but also don't approach an editor before you're ready. Once when it took me a paragraph to describe an article I was writing, a colleague said, "You've got to sound bite it, Mary." The same goes for your book. If you can't say what the major point of the book is in a sentence or two, you're not ready. If you can't provide a concise summary of the book and its importance in a paragraph, you're not ready. How do you go from writing the project to pitching it? A good exercise is to take friends to lunch, perhaps friends who know nothing about your project, and explain your project to them, until you can explain it to a new person in a concise, interesting and powerful way. Then you're ready to approach editors at conferences, and to write follow-up e-mails.
I try to begin a book proposal with one paragraph (or two) that will hopefully cause the reader to want to read the rest. I do the same thing in an initial e-mail or letter to an editor (or an agent, if that's what you're looking for). These folks are very busy, and many projects cross their desks. Let them know that they can't put yours aside in the first page of anything you send. Don't hide the crucial findings or dramatic nuggets on page five. By then, your carefully written proposal may have been set aside. In case it's helpful, here's how I began the proposal for the book I'm working on now:
In 1960, a year of tumult and change in both Africa and America, America’s leading civil rights lawyer, Thurgood Marshall, was caught up in race politics on another continent. Invited by African nationalist leaders to help write Kenya’s independence constitution, he would find himself protecting the rights of a new kind of minority: white landholders soon to lose political power. Meanwhile, the fight for civil rights at home would change, as student activists began a sit-in movement and hoped to push the older generation of lawyers aside. Before long, Marshall would become the Supreme Court Justice we remember him for. The life lessons he would take to his work on the Court included his African journey, which reinforced his faith in law and minority rights as a way to perfect democracy. Marshall would tell everyone about Kenya. But the story of his work in Kenya has never been told.
There was, of course, much more to this proposal, but this is how it started out.
Finally, most of the time, it's best not to send a completed book manuscript, unless an editor has requested it. Most editors want to see a proposal and a sample chapter. If you send the full manuscript, it will probably take the editor longer to read it, and outside reviewers longer to review it.
Later in the summer I'll post about how to write a chapter outline for your proposal, and other topics.