By making a few simple lifestyle changes, you may be able to prevent tooth discoloration. For example, if you're a coffee drinker and/or smoker, consider cutting back or quitting all together. Also, improve your dental hygiene by brushing, flossing, and using a mouthwash daily, and getting your teeth cleaned by a dental hygienist every 6 months.
If your teeth appear to be an abnormal color for no reason and you have other symptoms, make an appointment with your dentist.