Query letters are important if you're going to even think about sending your work anywhere, be it novel or other. Writing a query letter is actually quite easy, you may be surprised.
I've been around the web and have seen many different ways and different guides to writing a query letter. So anyways, here's the basic layout along with all of the information you'll need to include.
Name (not pen name)
Title of work (in parenthesis state genre/s)
In the first paragraph give a brief summary of what the book is about. Be clever, because this is the first sample and idea of your book that agent or publisher will be reading. This would make it the hardest part of the query letter that you are writing.
In this next paragraph you are going to include the following information: Target audience (Young Adult, Middle Grade, Adult, etc.), note if the book will be made into a series, and if so list a brief synopsis (2 - 3 sentences at most) of entire series, list the legnth of the book (how many words is it?).
Note if you'll be needed an illustrator or not.
In the next paragraph include a bit about your background in writing, list anything that qualifies you to be writing, any experience, etc. You may not have much to put here, so just do the best with what you have.
Next, note what your marketing and promotion plan is. If you don't have a marketing plan yet, then you shouldn't be writing a query letter so soon in the game anyways. We'll be going more into marketing plans later.
Now this is your brief closing sentence, I usually put something here like "thank you for your time and consideration" be creaive, and be "professionally sweet".
Then you'll put Sincerely,
TA-DA! You've just written an awesome query letter! It all should be able to fit on your basic 8 x 10 piece of paper, keep that in mind.
Alright, so after you write your query letter, make you you edit and re-edit it, that is very important. If it has errors in it, it may just be rejected just like that, because errors are a sign of laziness. It's just one page, so make sure you edit it very well. Also, be sure to read the submission guidelines, you may have to add or remove sections depending on the publisher/agent, but usually this query letter works for everything.
After you've finished it's always comforting to get a second opinion, so feel free to send it to me, and I'll be happy to critique it and let you know what I think about it.