1. Never, ever, click on any links in any spam - especially not to "unsubscribe". All this does is confirm to the spammer that they have a "live" address.
2. Read any incoming emails in plain-text, never html. Html spam emails contain links to graphics and scripts on spammers sites, confirming your email address
3. Use a Disposable Email Addresses such as those provided by spamgourmet.com
4. When you sign up for something on the Web, there is often some innocent-looking text at the end of the form saying something like: "YES, I want to be contacted by select third parties concerning products I might be interested in." Quite often, the checkbox next to that text is already checked and your email address will be given to you don't know who.
5. Spammers use special programs that extract email addresses from Web sites and Usenet postings. To avoid ending on a spammer's mailing list when you post to a Web forum or a newsgroup by not using your real email address or use a disposable one.