I get a lot a compliment on my teeth being really white (not that I complimenting myself right now) but you should know that I have a strict regimen to take care of my smile.
What you should first know is that your natural teeth color depends on your genetics. Some people are lucky to have pearly white teeth while others have more yellowy tint. If you belong to the second category, don't expect any miracle results from my advice. The below will only help prevent your teeth from getting any stains or yellow tint but it cannot dramatically change your natural color. If it is what you are looking for, you will have to go for a more radical solution and check with your dentist.
And don't forget that you are never fully dressed without a smile :)