Locate agents who represent authors who write in the same genre as you. One way to do this is to check an up-to-date copy of "The Literary Marketplace." Many libraries will carry this book, which contains a list of current literary agents and the genres they specialize in. You can also find agents by checking the Acknowledgments section of books that are in the same genre in which you write to see if they thank their agents. Compile a list of potential agents based on your research.
Look on the agents' websites to find out what you need to submit for query, or if they're even accepting new queries at the time. Check whether they want a single page query, the first 15 pages of your work or your detailed biography. See if they accept queries via email or if you must send it through the U.S. Postal Service or FedEx.
Tailor query letters and other submissions to what the agents request. Make sure your letter address everything the agent wants, be it a description of your work, your background, your thoughts on potential marketing, etc., but avoid sending too much. If they do not request the first pages of your work, do not send it.