Instead of rinsing with a conventional mouthwash, purchase a low-alcohol one especially formulated for dry mouths. Regular mouthwash is high in alcohol and will compound the problem.
Avoid using over-the-counter antihistamines and decongestants, which dry out mucous membranes, including in the mouth.
This is one of the easiest dry mouth remedies. If you tend to breathe through your mouth, try to train yourself to breathe through your nose.