From what I understand, you dont want to just crank the voltage up, thats the easy way to smoke your chip.
From my limited knowledge:
1) turn down all your multipliers. ( ram,gpu etc...)
2) SLOWLY turn your cpu multiplier up.
3) reboot
4) continue this process untill you cant reboot the rig, or you reach your goal. If you are not satisfied with the mhz you have achieved, you can SLOWLY start to raise the voltage in .05v increments. until it is stable, or you burn up your cpu.
once your done, slowly bring your other multipliers back up for your other components, e.g. your ram. Then reboot to see if it is all stable.
Last but not least, run a benchmark on your cpu, ram, etc to make sure your system dont crash.
This is what I have been lead to believe in my very limited exposure to the "hobby side" of computers. I would by no means follow this word for word!
-Chris