Writing a query letter is a science and an art. But really, it's way more science. Boiling an entire novel down into a few sentences can be nightmarish at best, and editing those sentences with an outsiders point of view (one who doesn't know that the race of evil creatures in your book are called urgles and their king is just a costumed human imposter) is even harder.
Cue agentqueryconnect.com - the most helpful resource I've run into for workshopping the never ending Query plight. It's a simple site. People post their queries, their synopses, and the first 150 words of their novel (all in different forums) and other novelists (just like you) take a crack at editing them. The more you edit, the more you get reviewed. It is that simple, and that helpful!
If you have written, are writing, or even thinking about writing a novel, I implore you to check out this awesome online space. I've never seen anything more useful for a burgeoning writer online.
Feedback. It is invaluable!