I incrementally raise the voltage at stock speed whilst noting the temps under load until things get a bit toasty, this gives me an idea of the voltage I can put into the cpu. Then I start increasing the multiplier, again noting temps under load, until the system becomes unstable. Once this far I have a decent overclock and can continue tweaking the speed upwards whilst testing for longer periods and trying out other adjustments which people on here have posted about.
This might not be the "proper" way to do it but at least it quickly gets me to a stable overclock with minimal bootup failures.