Make sure your book is marketable in other countries. Nonfiction and self-help books are the best candidates.
Attend the Frankfurt International Book Fair, or have an agent do so. It is a huge book fair in Germany held for the purpose of buying and selling foreign rights.
Make a list of foreign publishers that might be interested and send them information about your book. Provide the information manually or direct them to a website with all the pertinent information.
Hire a foreign rights agent if you don't want to negotiate the book deal on your own. Locate these agents on the Internet using a database such as Agent Query, or by using a book such as Writer's Market or Literary Market Place.
Read the publishing agreement carefully. Make sure it covers things like duration of the license, territories the publisher can distribute to and rights granted for specific formats.
Do not provide the foreign publisher access to the book until you have received the signed publishing agreement and the advance.
Hire a translator yourself if you don't want to give up any rights to a foreign publisher. Search the websites of professional translator associations such as the International Federation of Translators or the American Translators' Association