I read this a while back and used it to overclock an older Intel Xeon. It's been updated for newer processor and still is the best overclocking guide I have see.
Full guide here.If you want to squeeze every last ounce of processing power out of your new computer or aging system, overclocking is a great—if slightly nerve-racking—option. Here are some simple guidelines for safely overclocking your processor.
Simply put, overclocking your processor (or CPU) involves running your processor at a faster speed than was intended out of the box. While overclocking, at its core (no pun intended), can be quite simple, there's a bit more to it than just tweaking one setting. The harder you push your processor, the more voltage you need to give it, because without enough power, the CPU can't run fast enough. However, higher voltage also means higher temperatures, so you need to be careful not to overheat your CPU, which can lower its life, not to mention fry it completely if you aren't careful.