Find the website of the literary agency you want to query on-line and read their submission guidelines carefully. If they do not have a website, look the agency up on Publisher's Marketplace or Agent Query. Each agent will have his or her own specific guidelines, and it is important to follow them carefully rather than waste your time mailing the wrong information.
Open a word document and type your query. Include your contact information as a left-justified header with your address, phone number and email address. Address the agent by name, such as "Dear Ms. Black." Never use a generic opening like "To Whom It May Concern." Write your query in three paragraphs; the first as an introduction explaining the title, genre and average word count of your novel, the second as an enticing blurb that does not give away the ending of the book (much like the blurb on the back of a published novel), and the third as a short bio related only to your writing career, including relevant degrees, other published works or writing awards you have won. Type your name, then print and sign your name in black ink. The query should fit on one printed page.
Print a full synopsis and/or the first few pages or chapters of your novel depending on the requirements of the agency as stated in Step 1. Some agencies may only want the query, in which case you can tri-fold the query letter and place it into a standard 3 x 6 inch envelope. If the literary agent requires several chapters and you have a thick packet to mail, choose a 9 1/2 x 12 inch envelope. Never mail your entire novel to a literary agent unless he specifically requests it, as it does not guarantee he will read it.
Place a self-addressed stamped envelope (SASE) in the package with your query. Literary agents require these and you will not receive a response unless you include one. Mail your query via regular mail or, for larger packages, media mail.