- Don't use your main email address to sign up to lots of random websites. Sometimes it is best to use an alternative account for those purposes.
- Don't post your email address anywhere in plain sight (on your website, etc.) Use a contact form instead. Spammers love to grab email addresses from websites.
- If you are using a contact form, make sure it has some form of captcha (enter a code to make sure the user is human).
- Less important: If your email address is somewhat easy to guess in random (ie. email@example.com), consider using something more unique (ie. firstname.lastname@example.org).
- Unsubscribe to any newsletters you don't want to see by finding the small unsubscribe link on the bottom of emails.
If spam is still a big problem, the best spam filter out there is Gmail. You will get virtually no spam at all.