Drink only water.
Besides the fact that soft drinks will give you unwanted calories, they will also stain your teeth. Coffee and tea are one of the worst. So to avoid adding more stains to your teeth, start drinking water instead of the alternative. Water is good for you and will not leave you dehydrated like sodas will. It will also not add anymore damage to your teeth either. Switching to just water might be difficult, so just try giving up a soda a day until you have changed to water.
Many people think they have to undergo huge expenses to have a whiter smile, while this is not the case. You can purchase whitening strips at most local stores for a decent price. By just using these a few times you should start to see a difference in your smile. If you have sensitive teeth you may not want to do it as often as it recommends on the box. Just try skipping a few treatments until your teeth stop feeling so sore. From personal experience I have noticed the biggest difference with the Crest Whitestrips.
If you are still having trouble with getting whiter teeth you can always talk to your dentist about veneers. Veneers can be very expensive buy since they are put on top of your teeth, they can give you an amazing white smile. But be aware veneers do not last forever, so you will eventually have to replace them. Before getting them make sure that you are in a good enough financial place to afford having veneers.
A zoom treatment is where UV rays are targeted directly onto your teeth to give you a brighter, whiter smile. The results can be seen almost instantly, it continues to work even after you have left the dentist office. The only drawback is it isn't usually very cheap. Also while it works great, if you have sensitive teeth it can be very painful. Your teeth might can handle the first couple of treatments but then after that they can start hurting and become extremely sore. So if you know that your teeth are already sensitive, it might be a good idea to try one of the other ways to get a whiter smile.