You can replicate the expensive tooth whitening mouthwashes with just a few basic ingredients: To a 32 ounce bottle add 1/4 cup peroxide, then top off with water. Add 1-2 drops of mint extract, shake and taste to see if it is minty enough. If not, add extract just one drop at a time until the desired intensity is reached.
Use this mouth rinse once a day, before brushing your teeth. Do not swallow it! Your teeth will gradually become whiter, but remember that tooth enamel has a natural color. Your teeth are not supposed to be glaringly white.
PS. I was going to put a photo of white teeth here, but all the images I found were kind of scary. So think of a pleasant smile with white teeth.