First of all its necessary to know about any habits.
Pan , Gutkha, smoking ,tea or coffe etc.
If you have any one of the followings staining to the teeth is quite natural in general.
So you have to stop or decrease the frequency of your habits.
Secondly your Diet quality.Fast foods , junk foods, beverages, sticky food material also may stain your teeth. Because they enhance the chance of formation of palque.
Next Steps
you brushing habits must be improved.
you must use soft brush with tooth paste that must contain sufficient amount of abrasives.
you must use non alcohol based mouth washes. But long term use may again cause staining.
Health Tips
Go to your nearby dentist .And ask for Oral prophylaxis ( scalling/wash/cleaning).
But if your problem still persist you must consult to a periodontist.
long term plaque and calculus may decay your teeth and may start formation of Dental caries.
Hope your problem may resolve soon.