Saliva condition and flow are two main reasons for dryness of the mouth and it is a very common problem. But you can find its solutions by home remedies for dry mouth.
Take cayenne pepper powder and use it to rub on your tongue and around areas of the mouth. It will create burning sensation but would be very effective in activate savory glands.
Extract juice from fresh Aloe Vera leaves and drink this juice daily. It will be very good to reduce dryness of the mouth.