1. Please don't write to ask me what was wrong, or what you need to do to improve. I delete those emails without answering despite my loathing for such rude behavior. More than once or twice I have tried to "be nice" and help people. It NEVER works out. And I've never taken a project on after rejecting it. What that means to you is you should spend your time querying other agents, not trying to figure out why I didn't like it.
2. Don't write back to thank me for looking at a query. It's my job, you got a form letter, enough already.
3. Don't ask me to refer you to someone else. If I think there's some one else better suited for you, I will suggest it on my own. I don't respond to those emails either.
4. If I do suggest you query an agent, do not ask for his/her email address or contact info. If you can't figure out what it is on your own, you've got a problem. The reason I don't give out email addresses is cause many of us have addresses we use to talk to each other, or colleagues, and different ones for querying.
5. You just have to get over the idea that "it's not right for me" is some sort of comment on the value or quality of your work. It's not. It's only a comment about whether it resonates with me AND whether I can sell it. I pass on really good stuff all the time.