A good place to start is setting up the gamma on your system correctly. Usually there is a utility to do this related to your video card. If not, you can get decent results from http://www.photoscientia.co.uk/Gamma.htm

If you don't have this right, none of the rest is going to make the first bit of difference. And you may THINK you have adjusted it, but it bears revisiting and VERY careful attention. Ask me how I know.