Find a reputable on-demand publishing company. This is the most important step in the process. Interview several companies until you are satisfied with the balance of cost and services the company provides. Ask to see samples of their finished products.
Choose the level of editorial and design service you need. Most on-demand publishers offer several levels of service, ranging from no-frills to full-service. Avoid the tendency to think that having your spouse check the manuscript for typos is enough of an edit. Spend as much money as you comfortably can on this step. If your content is sloppy, it won't matter how well it's marketed.
Identify the appropriate marketing and distribution services you need. Again, you will likely have to choose from several levels.
Study the contract carefully. Understand who owns the rights to your manuscript and make sure you're comfortable if it isn't you. Traditional publishing houses typically purchase the rights to a manuscript in exchange for providing an advance payment to the author. With most on-demand publishers, the author retains rights to the manuscript (with no advance).
Verify that your publishing package includes tasks such as obtaining an ISBN and filing for copyright. If it does not, you will have to do these things yourself. To obtain an ISBN, contact the U.S. ISBN Agency (Bowker) to apply. As for copyright, you technically own the copyright the moment the book is written. To apply for an official copyright, contact the U.S. Copyright Office. Both of these agencies are listed in the Resources section.
Submit your manuscript according to the publisher's process.