This is an issue for many individuals out there, including mouth breathers. Smokers and those on medications. The main idea is to keep your mouth and self hydrated, so drink fluids, especially water. MI Paste, Biotene, etc., are available through your dentist or pharmacist. Refrain from smoking and alcohol. Don’t rinse with a mouthwash having alcohol (as this dries your mouth). Don’t place a candy under your tongue or in your mouth at bedtime (causes cavities). Unfortunately, there is no panacea to resolve this.
Combating dry mouth involves stimulating salivary flow. This could be as simple as substituting one medicine for another, or eating/drinking something that can stimulate flow, such as citrus flavored hard candies (sugarless), or using specially designed mouth rinses, such as Biotene, Oxyfresh, or others. Good luck.
Hope this helps!