Avoid beverages that can leave stains on your teeth if you want them to be white and bright. This includes coffee, soda and tea. Alternately sipping water with these drinks is an effective way to reduce your risk.
Use a straw when you are drinking any dark liquids. Straws make it so that liquids have less of an opportunity to cause tooth stains. In fact, usually the liquid will bypass your teeth completely, instead going straight down your throat.
Brush your teeth at least twice a day. It might seem like an obvious thing to do, but most people neglect to brush their teeth as well or as often as they should. If you don't bother to brush your teeth properly, they are unlikely to remain as white as you would like.