Okay you should now have a decent OS install. One way to have a great base for gaming is to configure a specific Game Hardware Profile an article about setting this can be found here. This is ideal for your hardcore gamer, who will reset their PC to get the best out of their game. A lot of people a reset to play a (perhaps not so taxing) game is overkill. However there are utilities out there that will close unnecessary services whilst you are playing. The people behind this site (niris.co.uk) have a free utility that does just that, find it here
This is normally as far as most people go, but if you wish to get more involved in your hardware, the next step is overclocking. Overclocking is the process of running your PC components faster than they are rated. Typical components are your CPU and your graphics card. Check out the following links:- TomsHardware - ExtremeTech - Anandtech - TweakTown - ExtremeOverclocking, for more info.