I've only used MSI Afterburner as a GPU overclocking software and it works great. Without adjusting any voltages yet, try raising the core clock speeds slowly and test with Furmark (stability and temps) and any fast 3D benchmarks (to see if there are any artifacts or not). If it's not stable, raise the voltage. Next it's just repeat until you're satisfied and/or you've reached the max safe temps or speed.
Thanks. I did find a guide that said pretty much the same thing but it was a few years old and I just wanted to make sure that's still what people use.