There are many remedies in the pet store for dry skin on dogs. He may have allergies also that would require a visit to a vet. Most of the remedies require adding a supplement to their food. You can add omega 3 oil or simple vegetable oil. It takes a few months to see an improvement.
Aloe vera is a good treatment for dry skin. Beware of the chemicals involved in any cream, since your dog will probably eat some of it, but aloe vera that's safe for children is probably safe for the dog - always double check before buying.
Regular use of acv in your dog's diet can help prevent skin rashes, skin irritation, tooth decay, infections, and tear stains. A teaspoon added to water or food 2–3 times a week should suffice as a preventative measure.