2. When possible, avoid e-mail attachments both when sending and receiving e-mail.
3. Configure Windows to always show file extensions. In Windows 2000, this is done through Explorer via the Tools menu: Tools/Folder Options/View - and uncheck "Hide file extensions for known file types". This makes it more difficult to for a harmful file (such as an EXE or VBS) to masquerade as a harmless file (such as TXT or JPG).
4. Never open e-mail attachments with the file extensions VBS, SHS or PIF. These extensions are almost never used in normal attachments but they are frequently used by viruses and worms.
5. Never open attachments with double file extensions such as NAME.BMP.EXE or NAME.TXT.VBS
6. Do not share your folders with other users unless necessary. If you do, make sure you do not share your full drive or your Windows directory.
7. Disconnect your network or modem cable when you're not using your computer - or just power it down.
8. If you feel that an e-mail you get from a friend is somehow strange - if it is in a foreign language or if it just says odd things, double-check with the friend before opening any attachments.
9. When you receive e-mail advertisements or other unsolicited e-mail, do not open attachments in them or follow web links quoted in them.
10. Avoid attachments with sexual filenames. E-mail worms often use attachments with names like PORNO.EXE or PAMELA_NUDE.VBS to lure users into executing them.
11. Do not trust the icons of attachment file. Worms often send executable files which have an icon resembling icons of picture, text or archive files - to fool the user.
12. Never accept attachments from strangers in online chat systems such as IRC, ICQ or AOL Instant Messenger.
13. Avoid downloading files from public newsgroups (Usenet news). These are often used by virus writers to distribute their new viruses.
These tips are provided by F-Secure.