Keeping your Windows PC safe online and on a network requires you to keep Windows, and your software up to date by running Windows Update and installing the latest version of your software.
You also need a firewall. You can just use the Windows 7 or Vista firewall which is built-in to 7 and Vista. But, if you use Windows XP, it is best to use a third party software firewall like Comodo firewall since the XP firewall does not has outbound protection.
It is also important to keep your anti-virus and anti-spyware up to date. Also, make sure to scan your computer on a regular basis. I recommend Free Avira Anti-Virus, and SuperAntiSpywarepaid edition since it comes with a built-in active spyware shield, automatic updates, and schedule scan which the free version lacks. Make sure to scan your PC on a weekly basis.
I also recommend you keep your Web Browser and its Plug-ins/add-ons up to date which is very simple since it is usually done automatically, or you have to click an update now button. Make sure your version of Java and Adobe Flash Player is up to date.
It uses LinkScanner technology which scans a website for security threats before you visit it.
(suggestive)MyWot.com Plug-in is a great plug in to tell you if a website is safe or not. If it is not safe, the plug-in will turn Yellow or Red. It is available for Internet Explorer, FireFox, and Google Chrome. It has a high rating on many reviews, but Mywot can be used to slander websites which are competitors to another site or if the user does not agree with your point of view. He can just rate you down and leave a false comment on your Website profile..
NoScript.net has a great plug-in to keep you safe from dangerous scripts like Java, Java-scripts, Flash, and ads from infecting FireFox.
I also recommend you download software from trusted sites like SourceForge.net instead of random websites you find online. You wouldn’t eat food from unknown sources, so why should you use software from unknown developers with no track record of being safe like CCleaner. Also, avoid downloaded pirated media files since they can contain viruses, and spyware. Buy your music, movies, and pictures from a store. The best way to stay safe online is to avoid fishy websites like Porn, piracy websites, and file sharing programs.
By keeping your PC safe, your network and internet speeds should also improve since some virus use your network and internet connection to spread the virus to other PCs and it can slow down your overall network performance.