Keep your operating system updated/patched. Set it to "auto update". Use anti-virus and anti-spyware software and keep them updated. Do not visit un-trusted websites or follow links provided by unknown or un-trusted sources.
Secure your transactions. Look for the "lock" icon on the browser's status bar and be sure "https" appears in the website's address bar before making an online purchase. The "s" stands for "secure" and indicates that the communication with the webpage is encrypted.
Be cautious about all communications you receive including those purported to be from "trusted entities" and be careful when clicking links contained within those messages.
Do not respond to any unsolicited (spam) incoming e-mails.