I am in the process of playing the literary agent game at the moment. Everyone has a different idea of a great query letter formula. After researching and rewriting and perfecting for over a year now the best formula and break down (basically query letter for dummies) is found on a page I follow. He has a lot of wonderful information on his blog. I would reccomend starting here. Normally if you have a question it can be answered on his page.
Good luck!
This is the link to the query letter formula
Nathan Bransford - Literary Agent: Query Letter Mad Lib
The link to his home page is:
Nathan Bransford - Literary Agent