Baking soda will clean your teeth, but (in pure form) can be rough on tender gums. Some people will recommend Hydrogen Peroxide to whiten teeth; this, also, has harsh side effects when used regularly. Most teeth whitening kits are unpleasant to use and may cause other problems.
Regular dentist visits and normal use of a quality toothpaste (many brands offer whitening formulas) is the safe way to go.