So you've finished your dissertation. Your committee has approved it. Now you can just box it up, send it to a publisher, and receive a book contract, right?
In reality, even the best dissertations must be revised before being accepted for publication. Because they receive so many unrevised dissertations a year, most editors can spot one soon after opening the package. To guard against an immediate rejection, you'll need to spend a lot of time rethinking and reworking your manuscript. The press's acquisitions editor, the expert readers to whom the press sends the manuscript for evaluation, and the editorial board will all be evaluating not only the validity of your argument and the depth of your research, but also the book's potential appeal to a substantial number of educated lay readers outside a narrow field of interest.
The first step for you is to take a look at your topic. Is it interesting to more than just a handful of scholars? Is it unique? Is it timely, but not faddish? Where does it fit with other books published lately in your discipline? Chances are you'll have to broaden it, or narrow it, or take a different angle on it than you did in the dissertation.
Some quick and easy revisions:
Derricourt, Robin M. An Author's Guide to Scholarly Publishing. Princeton: Princeton University Press, 1996.
Germano, William P. From Dissertation to Book. Chicago: University of Chicago Press, 2005.
_____. Getting It Published: A Guide for Scholars and Anyone Else Serious about Serious Books. Chicago: University of Chicago Press, 2001.
Harman, Eleanor, et al., eds. The Thesis and the Book: A Guide for First-Time Academic Authors. 2d ed. Toronto: University of Toronto Press, 2003.
Lanham, Richard A. Revising Prose. 5th ed. New York: Longman, 2006.
Luey, Beth, ed. Revising Your Dissertation: Advice from Leading Editors. Berkeley: University of California Press, 2004.
McMillen, Liz. “A Doctoral Dissertation Is Not Yet a Book, Young Tenure-Seeking Scholars Are Told.” Chronicle of Higher Education, 5 February 1986.
Also, various university presses have author guidelines that will help you focus on matters most important to that particular press.