Following are few tips which you can do to keep your teeth white:
Avoid Coffee, smoking, tobacco, or anything that stains
Brushing 3 times a day, (after every meal) will greatly help you be removing stains before they set in.
Brush gently, harsh brushing with a lot of pressure will only weaken the surface of your teeth.
Drink tap water because it has fluoride in it, helps build protective layer on your teeth.