Great post at 43 Folders on how to make your e-mail worthwhile and manageable for the recipients:

Before you type anything into a new message, have explicit answers for two questions:

1. Why am I writing this?
2. What exactly do I want the result of this message to be?

If you can't succinctly state these answers, you might want to hold off on sending your message until you can. People get dozens, hundreds, even thousands of emails each day, so it's only natural for them to gravitate toward the messages that are well thought-out and that clearly respect their time and attention. Careless emails do not invite careful responses.

Think through your email from the recipient's point of view, and make sure you've done everything you can to try and help yourself before contacting someone else. If it's a valuable message, treat it that way, and put in the time to making your words count.