Clean glass is important if only because dirt and other problems are more obvious on window glass.
There are any number of glass cleaners available, most of which contain ammonia, that do a good job of cleaning glass. Home made recipes are popular and effective however. 1 gallon water Others insist plain water is best, and some go to the trouble to use distilled water or collected rain water. A thorough glass cleaning is actually a three part process. First, wash the glass with soap and water along with the rest of the car.