Here are a few things to include in your query:
- Include some market rationale
- Let the editor know why you have chosen to submit to her and why
- Mention why you think your story would suit the publishing house or fill a market need
- You may want to compare it to something similar the house has published
- Show how it fits a them or topic that the house is interested in
- Respond directly to a comment the editor has made (or a comment in the market listing) and show how your manuscript answers to this comment
So that's it for now. I've got some serious writing to do. I need to finish my query letter.