Test renders I always do at 800x600 at 72 dpi(or smaller) when I am satisfied , a render at 1024x768 to check the final problems I took out and when I am completely satisfied everything is positioned ok I make a final render at: 2000x1500 at 300 dpi ,that usually gives a great result, specially if you want to print it in a big size. Be aware though, If you have a multiple character, lots of lights scene, it could take a lot of time to do this, usually I let these render at night(or during footbal)and postwork the next day.