I've been clandestinely working on a query letter for months now. Perhaps even since I first started writing the novel. For purposes of being mysterious, I'm going to call that novel Jordan Valley in these blog posts, but that is only its working title. I have a secret one I prefer and hope ends up being the published title.
After I had the novel written (which was by last spring) I started crafting a pitch for it. I kept it to 200 words, even though I know a pitch is often only a 100. I re-wrote it several times, then had a friend review it, then worked on it again. A few weeks ago, I took that pitch and started to write it into a query letter.
Janet Reid suggests a good query letter will take about two months to write, with several iterations. I guess one could say I've been working on this one for about that long, if you count the number of times I re-wrote the pitch. I've used most of that pitch in the query, but restructured it to fit the format Reid suggests.
If you haven't encountered Janet Reid, and are attempting to query a novel, I don't know where you've been. Her blog Query Shark is indispensable. There is a lot of information online about how to write a query. Reid offers a lot of information of how not to, and that's actually more useful. There are hundreds of queries she's critiqued, and also many of them give multiple iterations, so you can see how the author evolved the query with Reid's help. A lot of it may seem like common sense, but obviously there are a lot of people out there writing bad queries. And although a good query doesn't guarantee a book deal...it certainly helps a great deal.
I'm still working on it, and then it's going to go to a lot of people before it goes anywhere near an agent. Because that is how you do it.
[Also, because that's how long it's going to take me to work up the courage to actually send the damn thing out to anyone.]