1. What I like to do is, in BIOS, start by keying 'F5' and loading optimized defaults. Reboot into BIOS.
--When I was first learning, I kept voltage settings on the 'Manual' range instead of 'Offset.'
2. I went down the line and replaced all of the 'Auto' with the value that the machine selected for itself. Reboot into BIOS.
3. Next, I scroll down to the voltage settings and change ONE setting ONE step down - usually CPU voltage - by simply pressing the '-' key one time. Reboot to OPERATING SYSTEM.
4. I use Realbench because I am lazy, and it does what I need, on the Stress Test tab for 15 minutes. If my machine doesn't crash or freeze, reboot to BIOS.
5. Rinse and repeat for all of the voltage settings, saving the semi-stable (only stressed for 15 minutes) BIOS settings each time before changing anything.

6. Now that all of my voltage settings are as low as they can be for the current clock speeds, I go to RAM clock/timings, bus speed, CPU multiplier - in that order, changing one setting at a time and following up with (you guessed it) 15 minutes of Realbench stress testing.

7. Eventually (it took me 6 months on my old CPU) you'll get everything capped out for your machine, or at least where you want it. At this point, I run the Realbench stress test for its maximum duration. If my system survives that, I run the Furmark GPU stressor and Prime95 blend simultaneously for a day or so.

8. If your system survives that, then congratulations!! You can now get another CPU or component and start the process all over again!!!

Z

Edit:
This is NOT necessarily the best way, but it is MY way.

Also, sometimes I'll run the Realbench stress test for 30 minutes instead of 15, just because; and, I also periodically (especially when messing with RAM settings and bus speeds) run 4 iterations of MEMTEST 86.