There are simple methods available on Google but to get a true calibration you have to run it with a hardware piece commonly called a "spider". It makes sure all your pixles are showing true colour by taking a range of samples and adjusting temperatures, contrast, and brightness through your comp.

Once it is set you can run it a few days on an LCD then want to run a check every couple days, on a CRT usually two weeks is good but I tend to check mine weekly just in case. I usually start it up as I am leaving the house so I don't have to sit around and wait for it to finish.