Hello I am one of those people who like to raise the numbers one step at a time and test the results for stability.
By this I mean I will raise each field up to the next available setting leave it like that and check for system stability and heat output.
I also use 3DMark06 a lot to benchmark the results. 3dMark06 http://www.futuremark.com/benchmarks/3dmark06/introduction/
Once I hit a combination that starts causing issues, I step it down a notch and try again.
I do not know about anyone else, but there is no exact formula with over clocking that works from board to board, sometimes what works for one motherboard does not work with another, even if both systems are exact duplicates of each other.
I have tried this when I was assembling two systems that had exactly the same setup, I could not get both machines to work with the same exact ratios.
Part for part, both computers were exact duplicates.
So as I said, you have to experiment with the settings, stress the system, see if it is stable, if so, try the next setting the BIOS allows and stress the system again, until you start to see either system becoming unstable, or the results offer no change.
Just remember, as you increase the ratios the system will start heating up and require a better means of getting that heat out of the system.
Also read this.http://www.wikihow.com/Overclock-a-PC