Smoking and coffee are the causes for stains and yellowish teeth but this does not mean that one should stop smoking and drinking coffee there are means of whitening the teeth. The first measure is to brush the teeth thoroughly everyday. Otherwise, there are products that help to get rid of the stains and there are clean up procedures that the dentist usually performs to clean the teeth.

Coffee is not that hazardous as smoking is. It is smoking that has a larger share in getting your teeth yellow. There are toothpaste and gels that can whiten your teeth again. Try using them and control your smoking habit.

There are special treatments which you can try. They clean and brighten your teeth. I think they are performed by most of the dentist.
As for your habit of drinking coffee, I would advise you to stop it.