The best/natural way to make teeth white is not to stain them in the first place. Drinks such as dark soda, coffee, and red wine all contribute over time to staining teeth yellow. Additionally, smoking, is probably the worst thing you can do to your teeth.
Any dentist will tell you that "natural and safe" home remedies are mostly ineffective in removing actual yellowing that has built up on teeth over time. (Most will tell you that over the counter whiteners are also ineffective.) However, you can prolong the effects of professional whitening treatments by avoiding further staining afterward.