You've written a fantastic book, worked laboriously on your book proposal and now you're ready to start shipping out packages and firing off emails to agents and authors. Slow down, Seabiscuit! Before sending out packages, you must first send queries to agents or publishers for them to request your proposal. It is extremely important that you are querying the right people as well. (Consult The Writer's Market, which lists registered agents across the country with their specialties). You want to make sure your query lands in the hands of someone who is interested in your topic or type of book. Avoid agents who request fees to review your work. A "real" agent is paid when you go into contract with a publisher.
The query letter is a sales pitch, and it should be persuasive in seducing an agent to request your work. Avoid editorialized language. Sweeping statements of, "like no other book," "amazing tale of..." should be avoided at all costs. It will incite an agent to stop reading. Let the agent discern from your query that your writing and ideas possess such qualities.
There are three fundamental parts to the query letter: Why me? Why you? And what I intend to do. Following the tips provided in the post on proposals, your query letter can be an annotated version of your proposal, and two- to three-pages in length.
WHY ME? This is your time to leverage anything significant in your writing experience or education. If you're light in this area, then demonstrate your unique expertise in how it relates to your book idea. One of the biggest mistakes new authors make when submitting proposals, is they forget to "sell" the idea of their book. Ultimately, you want an agent to think, "I can sell this" and an editor think, "I can buy this." See your query letter as a version of a trailer for your book, piquing the interest of the agent and/or editor, so that you will receive that request for proposal.
WHY YOU (THE AGENT)? Here you show an agent or editor that you have performed your due diligence and are sending a query to someone who is interested in receiving your topic. Remember the agent you are querying is a human being, and the best way to make a lasting impression is by tapping into their humanist side - but don't be creepy with it.
HERE'S WHAT I INTEND TO DO. After reading this part of your query, the agent should feel as though you've just dropped the mic, and left him wanting more. Here, you briefly discuss your platform, what's available to you in terms of promotions, and what media outlets you have access to, to help drive book sales.
Your query should be sharp and succinct, that an agent will request your proposal as fast as she can hit the reply button of the email.