How to overclock my dual core?

I have a g31m-p21 motherboard, I read that its actually quiet easy to overclock with. I am only changing the fsb at the moment because i only went from 1.8ghz to 2ghz. But it still freezes. Even if i add more voltage it freezes. What am i doing wrong? I had it at 2.5ghz steady on my old mobo. And the temps are very low, in the 20's idle and barely to 40's full load.