But it would be easier if you asked me to explain the theory of relativity!!!!
Some simple tips though:-
Usually if your card is set to the default settings it should give reasonable settings.
Most graphics cards come with configuration utilities - learn how to use them
Visit the games sites and/or forums.
Read you documentation and manual of your card and games.
Visit graphics card site.
Warning!! Be careful if you try and "over clock" your card.
Do a text search - I found the following info using "google.com" :-
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=RNWE,RNWE:2004-28,RNWE:en&q=tweaking+graphics+cards
Hope this gives you a start
Regards
Peter
Once you have installed the graphics card and the driver, is there anything special you need to do or make sure of so that I can get the maximum benefit of the games I play?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic