Always Make Sure You Have the Latest Virus Protection
Viruses can do all sorts of nasty things to your computer and can also send all of your e-mail addresses and those in your address book to spammers.
So keep protected!
Never Reply to Spam
If you reply to spam, you have verified your e-mail address to the spammers and they will send it on.
So you get more and more!
Never Open an Unknown Attachment in an E-Mail
Unless you know the sender and are expecting it don't open it!
Never Open a Web Page in an E-Mail
There are lots of e-mails which try to get details of your bank accounts, PayPal accounts etc. Never open any of these pages from within the e-mail as this will often take you to fraudsters. If say the e-mail purports to come from PayPal, then open their web site in a new copy of your browser using the correct address, which in PayPal's case is www.paypal.com.
Only open a web page in an e-mail, if you know the sender and are expecting the mail.
Never open it, if it has anything to do with bank accounts, credit cards, PayPal, eBay or money in any possible way.