I'm with you, just as new to the site and haven't revealed my query here yet. So you're one step ahead in the bravery department.
I have submitted my Query letter(s), three versions, three different agents, two rejections with positive comments (subjective) and one, nothing as of yet and not holding my breath.
This site is extremely helpful.
So far I've learned: know your genre, and familiarize yourself with the agent you're submitting to, i.e., what genre they're interested in representing. And perfect your hook to reel them in. Keep it to one page, note your word count in the last paragraph, name a few titles similar to your MS, and the audience are you targeting and who might be interested in your subject matter.
Lol...I'm just regurgitating what I've learned here :) but wanted to be helpful.