Top ten things to mention in your query:
10. All your friends love your story.
9. Your story will be the next mega bestseller.
8. Your story combines the best of Rowling, Brown, Patterson, and Meyer.
7. The protagonist is perfection.
6. The antagonist is evil incarnated.
5. The names of your children and/or pets.
4. What you did on your last vacation.
3. You're certain the agent will be a perfect match for you because both of you loved Avatar.
2. You've made a collage of the agent's photos collected from the internet.
And the #1 thing to mention in your query:
1. I'll call you tomorrow to make sure you received my query.
Shared with tongue firmly in cheek :)