Need help Ocing my 6850!

Just got my msi r6850 cyclone pe installed, came with afterburner, and installed kombuster (benchmark). I've never dabbled in overclocking, but i'm willing to give it a go. This heat sync is ridiculous so what could go wrong?  
I really don't know where to start, and I'd rather not mess with the voltage unless its clearly safe to do so. All I really want to do is kick it up a few notches without getting too advanced!