Queries are hard, you guys!
I’m writing a query letter for my first book, and it is very difficult. You can think of a query letter as a text version of a movie trailer; it is a dramatic bit of text meant to entice the reader, packaged with basic details about the book–author, genre, length, etc–and a whole bunch of spoilers. Queries are generally not something that readers will see, and the agents and editors you send yours off to want to know what they’re getting in their book. If, for example, your dark fantasy about a paladin’s experience with slavery takes a hard right turn off into a bunch of kinky sex (ahem), the agent is going to want to want to know to that up front.
A good query letter tells the reader who the major characters are, which one of them is the protagonist and which is the antagonist, what the major conflict is, and where/when the book is set. Ideally it should also showcase your writing, be entertaining in its own right, and be about a page in length. It’s ad copy, basically, where the ad itself is considered to be a direct representation of the skill of the person who crafted the product.
Or, at least, this is what I think a query letter is supposed to be. It’s what my research tells me it is. The truth is, I’ve never done this before, and it’s kicking my ass. My lack of real world experience with the publishing industry is a big obstacle here, one I intend to overcome, just as soon as I stop quivering in the corner with the fear that I’m DOING IT ALL WRONG and will get put on the big scary blacklist that agents pass around to make sure that people who use the wrong font never get published. How do you know there’s no blacklist? Maybe they don’t tell you because you’re not in the club! (The paranoia isn’t an official part of the process, but that doesn’t keep it from being popular.)
I’m on my third or fourth draft of my query. I hope to have something ready to send out by the end of the month. Or, alternately, I hope that the Book Contract Fairy will leave a 2-book deal under my pillow if I’m a good girl. Clap your hands if you believe!
 Assuming your book has a protagonist and antagonist, and not an ensemble cast. If it has one of those, you need to be clear about that.