I don't know what car you have but you should go to
http://www.teamassociated.com and download the Tuning Guide for the TC3. This will cost £3 or 4 and details all the setup changes and what affect they have. Although your car may be different the principles will be the same.
In the same section they have the "RC Handbook V2" which is free but less detailed.
Another option is the XXX Main Touring Car Chassis Setup Guide which is pricey but probably the best resource to teach you about setting a car up.
www.apexmodels.com have it for £15.