To get started with your overclocking adventures, download RivaTuner from www.guru3d.com, click yes to install and accept the program configuration default. RivaTuner will create registry database which might take a few minute. Read the readme file while you wait, especially the FAQ.

Now you’re ready to begin, Let’s juice it up!

1. Set Fan Speed.
In Rivatuner, click the Cuustomize button in the target adapter box and then click the videocard icon to open a dialog box labelled “Low-level system tweaks.” Click the Fan tab and then place a check mark next to “Enable low-level fan control.” We want to see how far we can push the GPU, so we need to keep it as cool as possible. To do that, click fixed. Now push the slidebar all the way to the right (to 100%) and click apply. If the noise bother you, set the fan speed to a lower value (but realize that won’t be able to push your card as far when using a lower fan speeed). Apply fan settings at Windows startup, “place a check mark next to the box labeled “Restore fan setting after suspended mode, ” and click OK.

2. Adjust Core Clock Speed
Again, click the Customize button in the Target Adapter Box and then click the Videocard icon. Click the Overclocking tab and then place a check mark in the box labeled “Enabled low-level hardware overclocking. Take the software’s advice and reboot so that it can detect the default memory and core clock speed. Relaunch RivaTuner after the system restarts.
Click the customize button again and then the videocard icon to open the “low level system tweaks” dialog box. Place a check mark in the box labeled “Enabled low-level hardware overclocking. “Now use the core clock slider to begin probing the limits of your GPU’s core. If the core is stock-clocked, start with gross adjustments-say, 25MHz at a time (Note: The arrow keys enable more precision than the mouse).
Used a smaller increment if the card is already overclocked or if your system becomes unstable immediately. The idea is to find the system’s outer limit, once you’ve achieved that, place a check mark in the box labeled “Apply overclocking at windows startup, ” click Save, and then click OK.

3. Adjust Memory Clock Speed
This step is identical to Step 2, except you’ll now be adjusting the memory clock slider. You’ll also want to bump your clock in smaller increment this time-say, 5MHz to 10MHz at a time. A warning icon in the form of a yellow triangle with an exclamation point will appear if RivaTuner thinks you’re getting too aggressive, but this isn’t necessarily a sign that you’re going too far; you wont know that until you stress-test the system.
If the system seems stable, place a check mark next to “Apply overclocking at Windows startup, “click Save, and then click OK. Repeat your stress test for at least one hour. If you run into stability problems after adjusting the core or memory clock speeds, reopen the system tweaks dialog box, click the Overclocking tab, and then click default button to rest the card to its original values.

Source: MaximumPC