I was recently asked via Twitter to write a blog post about "finding the right balance between "vague" and "too much information" in a query.
A query is sort of like a movie trailer. It's supposed to grab your attention and make you want to see the movie. Similarly, your query is like a "trailer" for your book (kinda like a blurb on the back of a book). Agents look at so many queries in a day. You want yours to stick out and say "Hey! Read me!"
If there is too much information in your query or if it's too vague, it's rather likely that an agent won't pay much attention, quickly moving on to the next, because s/he doesn't have a good idea what your book is about. What makes it special and unique from the other queries agents look at every day?
If there is too much information (such as, including too many characters, too much description/setting, too many plot details, etc.), your query could become unnecessarily bogged down and confusing.
If your query is too vague (for instance, if it talks more about a character, or the setting), then we really don't know much about the plot--the glue that holds it all together.
I do have a couple ideas I'll list below that I think might be helpful. Let know :)
1. About twice a year there is a Twitter pitch party called #PitMad (usually following #PitchMadness). This a great way to practice pitching. You have 140 characters to grab an agent or publishers attention. Very challenging, but A LOT of fun! Some authors will often offer to critique the pitches before you tweet.
2. Try to summarize your book in a few sentences/paragraphs.
3. Ask author friends for a critique, or look for agents who will post critiques on their blogs.
Hope you guys find this helpful!