Before you submit anything, here are a couple of tips from Writer's Market.com:
Quick tip #1:
Always check a listing's website before submitting. Submission guidelines, subjects covered, and even contact information can all change at a moment's notice. So be ultra-professional and double check before making your submission.
Quick tip #2:
Focus on the main sotry and characters when writing your query and cover letters. Think of your query as similar to the description on the back cover of a book or DVD. Don't get lost in the details, but make editors and agents want to read more.