Well I suppose it would depend on the setting what would be the best settings to change there are settings like terrain detail or draw distance or Anti-Aliasing and Anisotropic Filtering which will filter and smooth out objects. These are things you will probably want to do on your own to get a feel for what looks best to you. However keep in mind that you have a entry level card and maxing out most games will not be possible for you.
In terms of overclocking I agree with Sid its more of a luck of the draw sometimes you have a chip that is more resistant to heat and you can push it a bit further. And yes pushing your GPU beyond its limits can shorten the life of the card.