If you already have a literary agent, discuss the potential sale of film rights to your book with him. If your agent is not already working to get you a movie deal for your book at the time of publication, ask him to do so.
Find contact information. If you are going to pursue a movie deal, you need to approach agencies and/or production companies to make your case. Hollywood agencies typically have book departments specifically set up to buy and sell film rights of books. There are also a number of independent production companies actively seeking material for film and television projects. You can find contact information by doing Internet searches or consulting industry directories such as Hollywood Creative Directory, Bluebook Production Directory, The Writer's Market, and the Guide to Literary Agents.
Write a cover letter and a one-page synopsis of your novel. The cover letter should be addressed to a specific person and department. The synopsis should be more than a dry summary of your story. It should begin with a strong "hook" to entice the reader. Outline the points that would make your book an engrossing film.
Query your contacts. Make sure you proofread and spell check your cover letter and synopsis before mailing it. Don't expect instant results. It may take several weeks or months for you to receive an answer.