Send as little email as possible. Do not send large attached files without prior consent by the receiver. In the body of email tell what the format of attachements is. Targeted distribution lists minimise unnecessary email and also allow automatic filtering by the receivers. When possible send message directly to a person rather than a group of persons.
Personal message is preferrable to distribution lists.
Do not send messages to other persons than those who really must have e.g. if an action is requested from the receiver. Send only one message about a topic rather than several. Send as few messages as possible. It is often preferrable to upload file to a WWW server and only send a note by email. Do not send large attached files at all before prior consent of the receiver.