As many people here will tell you (and I tend to agree), there is no real safe way to overclock.
The, quote, "safest", way to overclock is to dish out the money to have a store that offers overclocking services, such as Micro Center, overclock the computer for you.
However, in some cases it is probably more economically sound to purchase better hardware because overclocking WILL reduce the lifespan of your hardware.
I realize this probably isn't what you wanted to hear, but it's the best I have for you as I do not personally overclock.