Keep messages brief. An eight line email has a higher chance of being read than a 4 page message. Link to more detailed information on the web if need be. Think about your subject line. Talk to people, not at people.
Email is a personal, friendly, informal medium.
Don't send people electronic billboard ads. Make sure that if people hit the 'reply' button to an email, even on an announcement list, it will be read by someone and a response will be sent. This will help with data protection law and enhance response. Be aware of the difference between email announcement lists that only you can post to, and discussion lists which anyone can post to. Using the wrong type of list could be embarrassing.