Make sure to install a reliable anti-malware software program and that you update it on a regular basis. SpyBot, MalwareBytes, and Ad-Aware are all very good anti-malware programs and are recommended highly.
Install a firewall to protect your PC. A firewall is particularly important to PCs that are connected to the internet for long hours as this will help prevent a large percentage of Malware attacks.
Use an email client that employs a spam filter. This is because a lot of Trojans and other viruses are spread over the internet by using email as a medium. By having an email client it will create a filter that will provide protection to your computer from attacks this way.