If I'm completely honest, if you're not confident overclocking, then don't overclock.
Otherwise, ensure you have a good cooler then slowly increase the frequency and voltage in very small increments and benchmark, if it crashes go back 1 increment and you are where you want to be. Keep your case open with access to your cmos battery/pins to short mobo when it does become unstable.
Never short it while the machine is turned on, don't even think about it, remove power, (plug and flick switch) anything else connected which can provide power, then attempt to turn machine on a few times to get rid of any build up electricity, then either remove cmos battery or short the pins with the reset switch or a metal object.