If you want some general rules for keeping your computer secure
Keep all software up to date, not just the operating system, especially programs that have access to the internet (web browser, char prorgrams etc).
Consider uninstalling Java. Do you need it for a specific program? If not it's better to uninstall it. Last year it overtook Flash as the most attacked software platform.
The webbrowser is the biggest opening into your system, make sure you secure it. Here is a good guide for securing firefox but the tl;dr version for all webbrowser is, disable javascript, flash and Java. Disabling these 3 things will stop most browser exploits dead. Only enable them on websites you trust. Firefox has an addon called NoScript that will help with this.
http://www.ghacks.net/2012/04/06/an-in-depth-firefox-security-guide/
Did you hear about the 600,000 Macs that were infected with a trojan? It was because of Java, eithe uninstalling it or blocking websites from accessing it with an add on like no script would have saved those computers.
Don't run as root (admin in windows). Check if your account is an admin one or not. If it is, create another non admin account and use that.
And of course have sense when running or installing programs. Make sure you get them from legitimate sources i.e. only install Firefox from Mozilla's website. If you do need to run a program you don;t trust use virtualisation, VirtualBox for example, to keep your system safe even if it does turn out to be a virus.
Since you're using Windows you'll need to take extra care with some non executable files. For example pdfs and word documents can be embedded with scripts and macros to do bad things. Be careful when opening random pdfs and .docs that were downloaded from the internet. Agaiin, for best security open them inside a virtual machine like VirtualBox.