The most effective way to combat spam is to never give out your e-mail address aside from people that you personally know. If you must sign up for newsletters and other e-mail services and promotions, then it is better to create a separate e-mail address for those purposes.
Also, you need to have a critical eye so you can easily identify spam e-mails. Do not open spam e-mails, do not respond to them, and never click any link in the e-mail.