How to write a query letter

A short expert from my NaNoWriMo thread, in response to a question on how to write a query letter:

"The point of a query letter is to convince an agent to ask for more. You don't have to tell her everything, you just have to make her interested enough to look at your sample pages. 

A query letter is basically a sales letter. Think of it as if you were writing a letter to sell a toaster: Would you describe every detail of the wiring? Would you describe the coils? Would you explain how to push down the lever to start the heating unit? No way, you'd focus on what makes your toaster different and cool and totally the toaster you want to buy! You'd talk about how it stands out in the crowded toaster market and how it has features no other toaster can offer while delivering reliable toasting services.

This is a query letter. You're not reinventing the wheel and you're not writing a book report. Just tell the agent what makes your book unique and cool in the most succinct and engaging language possible."

ADDENDUM: Even though it's a sales letter, please don't use corny sales talk and DON'T talk about how many millions of dollars your books will make. This is literature, remember? Keep it classy.

This is now my official answer to this question FOREVER.