Some of the things to avoid in your query letter are obvious, but others are not. Here is a list of what to avoid:
• Don’t be self-effacing. It might be charming in person, but your query letter has to show confidence. If you aren’t sure about your experience or book idea, why should an agent or editor be?
• Don’t mention who has already received and rejected your work. No one has to know who rejected you. It’ll just make this editor or agent think twice about rejecting you, too.
• Don’t ask about money and deal terms. There is a time and place for everything, and money discussions are never mentioned until you are in contract discussions with a publisher.
• Don’t request advice. An editor or agent has to offer enough comments ...