There's a few things to remember when using email that'll make it easier for you and those you're communicating with to read and organise mail. Here's a few suggestions:
Keep to a single subject will make searching for information in archives much easier. Particularly for work purposes, only discussing the topic in the email title will make it easier to return to the information later. It's almost as easy to send several short mails as one long one.
Use descriptive subjects to make it clear what the email is about. Also, make sure that your descriptive name is set correctly; it's more useful to see “Jim Smith” on the header that just “jim”.
Only add necessary recipients to the To: or CC: lists, so that only those interested in the email will receive it. Don't send to a 20-member email list because you want five people on the list to receive it; you'll have five happy recipients but fifteen unhappy ones.
Keep your signature small to reduce bandwidth and avoid taking up too much space in people's inboxes.
Given a choice between HTML email and text email, send plain text by default, until you know that someone can receive attachments or HTML-ised mail.
Don't send huge attachments, as it puts a considerable load on the mail server, and the mail may be rejected by your recipient's mail server as too large.
Keep quotes in replies informative and neat, making sure that replies to replies are nested and its clear who said what!