After writing numerous query letters on behalf of our clients, here are some conclusions we have reached about what works:
1) A query should titillate agents, rather than leave them sated. Give them just enough to provoke interest and make them hungry to learn more.
2) Unless the book is non fiction and steeped in some knowledge you and only you have, the query letter should be about the book, not the author. Who you are doesn’t matter. What you have to sell does.
3) It should be somewhat cocky. Tell them what you’ve got and end with an expectation rather than a plea. (“I look forward to hearing from you.”)
4) Have a reason for contacting this agent (so the agent doesn’t think you’ve sent query letters to every agent in the book) EG: “Because you represented xxxxx (a book like yours) I thought this might be your kind of novel.”
5) If you are querying by e mail, always include a SASE or you’ll never hear back. If the agent accepts e mail, query that way. (Shorter time hearing back)
6) It doesn’t hurt to compare your book to books that have sold well: (eg: “Madman is a character-driven thriller in the tradition of Frederick Forsyth’s The Day of the Jackal and, more recently, Daniel Silva’s The Mark of the Assassin.”)
7) A query should never be longer than one page.
These are our thoughts as writers and editors on query letters, and here is a recently posted top ten list of query dos and don’ts from literary agent Rachelle Gardner: http://bit.ly/ahkKur.