Purchase the "Guide to Literary Agents" or use an online database that allows writers to query member literary agents looking for authors to represent (see Resources). Narrow down your search for a literary agent by reading the guidelines and deciding which agents represent authors who do the kind of work you do. Many agents handle a variety of material, but quite a few of them are particular. Make a note of your possibilities, then narrow that list down further by putting your choices in the order you will approach them.
Write a query letter to the agent using the information given in the literary resource guides. The letter should be no longer than one page. Don't ramble on about how good a writer you are or how eager you are to be represented. The letter should contain the literary agency address in the upper right hand corner and the salutation. Address the query to whomever the guidelines specify, as the name is written.
The first paragraph should be a brief introduction. Tell the agent who you are, how long you've been writing and a little about any prior published writing credits you have. Include only a few select accomplishments as a published author. Don't try to list everything you have ever had published.
The next paragraph should be about the manuscript you would like the literary agent to review to base his decision on whether or not to represent you or the work. Give a brief synopsis of the work and indicate whether or not it is available for immediate review. It's possible the agent may not be able to represent this particular work, but may like your writing well enough to ask to see something else.
Close your query letter by thanking the agent for taking the time to consider your work and let him know you look forward to working with him.
Sign your letter and be sure to include your full name, address, email address and phone number under your signature.