The email that I send out every now and then mentions the following points:
If in doubt, ask the support group for help.
"From:" addresses on emails can be easily faked, if there's anything odd about a message, don't trust where it says it's from. Learn how to see the real from address.
Never do something that an email tells you to do. If a message says "forward this to everyone you know," don't do it. If a message says "click on the link immediately," stop and think about it.
Think about whether the message makes sense. Is it strange to get a message from that person right now? Is it strange for them to send you that file?
We strongly recommend that you access your mail in "plain text mode." This removes most of the formatting from the message and makes it harder for a "bad" message to disguise itself. Contact the support group for more information.
I have about half the company convinced to use plain text, and about a third of the people can check the headers in Outlook w/out calling for help, but we still get a few calls a week (about 150 people).