How to get good vid on HDTV Plasma

I’ve got a 42″ Plasma HDTV 1080i and wonder how you get output from dvi or hdmi to work good on the TV. I have tried before, but no resolution that was selectable would look good at all on the tv. So i’m curious how you get a good resoultion to work with the TV and it look good. I’d actually like to try gaming on it.