Everyone seems to panic when it comes to queries, and I've never really understood it. Sorry. I realize this makes me a bitch. But I can't help it.
The thing is, a query is simply an introduction to your book. It tells someone what the book is about and who you are. Yes, it should be well-written. No, it should not contain anywhere the following phrases:
* "or you'll be sorry"
* "Harry Potter"
* "Lord of the Rings"
* "my Mom/Dad/sister/cousin/best friend said it's the best book they ever read" (unless said family member is a bestseller and/or litereary award winner)
* "guaranteed bestseller"
* "will make a great movie"
* "the squirrels helped me write it"
But really, that leaves you a pretty decent amount of leeway. Here's what you want:
1. Opening line. Do not make this a question. Just say something like, "I am seeking representation for my 82,000 word urban fantasy novel Personal Demons and think you may enjoy it", or something along those lines (inserting your own word count, genre, and title, of course.) It's good if you know something about the agent, or the editor. "I loved Book X, which you edited or represented, and it made me think you might enjoy my book" is good. But don't go on and on. Just say what you have to say.
2. Hook. This huge page of Miss Snark's hook archives should help you there, but essentially, you're just saying what your book is about. What makes it unique, in storytelling form. For example, here's a quick one I just came up with for a famous book:
When a young, naive girl is offered the hand of rich, handsome widower Maxim de Winter in marriage, she jumps at the chance. Practical considerations aside, she's fallen deeply in love with him, and can't wait to start her new life as mistress of Manderley, his ancestral mansion.
But life at Manderley isn't all she hoped. Reminders of Maxim's first wife Rebecca, who died under tragic circumstances, are everywhere, asserting an authority over the house from beyond the grave. The housekeeper delights in making our heroine look and feel foolish. And Maxim seems like a different person. As the shadows over Manderley grow longer, our heroine learns that some mysteries should never be solved...and some ghosts refuse to be laid to rest.
Now, this isn't perfect, by any means. Certainly if this were my book I might have different things about the story I wanted to emphasise--more Mrs. Danvers, maybe, or more of what's-his-name, the guy who had the affair with Rebecca, or the boathouse, or whatever. It's difficult to write a hook without using the heroine's name (but of course the heroine in Rebecca doesn't have one.) If I were actually sending it out I would play with the phrases a bit, edit it up, maybe add a little more about the heroine's shyness and insecurities.
But this is a starting off point. It says what the book is about, at its core. This is a book about a woman who marries a man and ends up in his creepy house while everything changes and she's haunted by the spectre of a dead woman. This is a template you can work with. Don't be afraid of it. You should be able to say what your book is about in one sentence, if you have to. Here you have ten or so. It takes some time and some messing about, yes, but it really isn't that hard. I promise.
(By the way, I highly recommend this as a writing exercise. Pick some of your favorite books and write hooks for them. It helps you pick out what's important when you're not as emotionally involved.)
3. A list of credits. Say what you can. Don't make stuff up. Don't use a self-published or Publishamerica book, they're not credits. And if you don't have any, don't sweat it. It's fine to say, "My work as a [bricklayer] has taught me how to be [patient and meticulous] and that really helped when writing this book". Or eliminate the paragraph altogether, that's fine too. If you wrote a historical, say how many books you read in researching it. If you wrote about a hospital and you're a nurse, say so.
But don't mention your dog, your cat, your children (unless the book relates osmehow to children), your spouse (unless your spouse is famous or has the disease you're writing about), or your hobbies (again, unless they're relevant.)
And that's all. It's pretty basic. You can play with the structure. You can pull out all the tricks in your little writing trick box to make that hook shine and sparkle, but in essence, it's just a couple of paragraphs, and you have plenty of time to polish it. I start writing basic hooks when I start the book, and I keep it simmering in the back of my mind off and on during the writing.
You know your story. You've told your story. You can certainly write a couple of little paragraphs!
And don't forget to check out Evil Editor for his hysterical query critiques as well. Definitely worth bookmarking.