Okay, first and foremost, I'm not an expert on query writing, but I have read some things and heard some things regarding query writing, so I thought I'd share what I've learned:
First and foremost...please...don't give the rest of us a bad name: I read in The Complete Idiot's Guide To Getting Published by Sheree Bykofsky and Jennifer Basye Sander that sometimes agents even receive "gifts". Someone once sent someone a pair of old shoes.
Okay...so, number 1. NO GIMMICKS.
Some agents/ publishers like things one way, another might like it completely different.
So, Number 2. CHECK AGENT / PUBLISHER'S SUBMISSION GUIDELINES TO KNOW PREFERENCES.
Tip: Read their blogs if they have one. Sometimes they even say.
I have heard conflicting advice on whether or not to query with one's pseudonym (pen name). Some say yes and some say no.
Again...check preferences to find out what each agent / publisher wants.
I haven't read this book all the way through, yet, but it's put out by The Writer's Digest (a respected magazine for writers) called Guide To Query Letters by Wendy Burt-Thomas. In the back of the book it has several references. It looks like it's a very helpful book. I'll be able to tell you more when I've read it.
Rhonda Morrow says the minute you get into the process of finding an agent or publisher your manuscript becomes a product. That is, it's something you're trying to sell, that agent will try to sell, a publisher will try to sell. The consumers are those who are going to buy your book (and in the end, those are the people who get on amazon.com or go visit bookstores like Barnes & Noble, pick up your book and pay for it). So you have to make the book sell able. You want to put your best foot forward.
Also, spell check and grammar check. Most word processors have at least a spell check. If you don't use it, you're shooting yourself in the foot. Also, WATCH YOUR WORD USES. Some words SOUND the same, but are spelled DIFFERENT and have different meanings from each other.
EXAMPLE HERE (arrow down to the first submission of this query).
So, Number 3: CHECK YOUR SPELLING. (You're gonna do that in your manuscript, why not do it also in your query letter, which is what the agent/publisher will see FIRST).
I remember before I got married people would misspell my last name. It was only a 5 letter last name, and me and my family were (are) always willing to spell it out. One of the most common mistakes was that the "V" in the name was always lowercase when people would put it in without asking us how to spell our name. We never lowercase the "V" in that last name. Why? Because originally, before put the first 2 letters and the last 3 letters together they were separated. The first 2 letters would be there, then a space, then the last 3 letters. To make things easier, all 5 letters were put together as one word.
In high school, I remember my byline in the high school newspaper was printed with a lowercase "V". I complained to the editor, who couldn't understand my problem. She said the "W" in her last name (which was supposed to be uppercase) was often lowercase, but it didn't bother her. I told her when people lowercase the "V" it changed the pronunciation of the name.
So, NUMBER 4: CHECK THE SPELLING OF THE AGENT/ PUBLISHER'S NAME(S).
Go to their website, double, triple check if you have to, but get that name right! That's one of the most common complaints I see made by agents.
They don't care if you don't see a problem with lower casing their "V" or "W" in their last names, if they want it uppercase, you uppercase those letters.
Part of a person's identity IS their name. It's how we know who is who. That's why some people are so protective of their names.
Based on what I've read, if you respect the agents and publishers (editors) in the world, they'll be more likely to give you a chance.
Happy writing and best of luck querying.
Have A Marvelous Monday!