Whether you run Windows, Mac, Linux or your own built-from-scratch rules-them-all operating system, it is important to follow these general security practices for your computer...
Know the security software available for your computer. If you use Windows, consider security suites from Norton, McAfee, Trend Micro, AVG or Kaspersky. These provide, at a bare minimum, a virus scanner but may also include a software-based firewall and a browser add-on which helps secure your internet browsing.
Know your network. You may have several devices on your home network without even knowing it. If you have a wireless network you may have computers, printers, mobile devices and home appliances on it. Each have a certain amount of access to each other when sharing the network. Only allow trusted devices on your network.
Know your perimeter. Bad people and software can get in through an insecure wireless network, a compromised computer or lack of firewall between your computer and the internet.