That depends on what is causing the dry skin. Consider a veterinary exam to insure your canine companion is not suffering from a medical condition that may require treatment. For simple, mild "dandruff", without any accompanying problems, there are several steps that may help.

Chose a premium diet for your pet. Diet influences overall health, including skin and coat condition. Some premium diets contain specific, balanced, fatty acids ratios that will frequently improve skin condition and reduce simple dry skin. In some situations, your veteriarian may recommend additional supplementation with specific fatty acids found in fish oil and/or borage oil to improve pet's skin and coat health. Not any type of "fat" will do. Vegetable oil, grease, butter or bacon fat are NOT appropriate choices. For best results, fatty acids called "Omega 6 & Omega 3" must be fed in specific ratios. Numerous "Omega" fatty acid supplements exist. Always use mild grooming products. Consider a skin and coat conditioner as well. Don't over bathe--this can cause significant skin dryness. In some cases, a shampoo that helps loosen excess skin flakes may be needed. Routine brushing and coat trims when appropriate may help as well. Expect to notice MORE "dandruff" for a few days after grooming. Bathing and brushing often loosen surface skin flakes for a few days or until the excess flakes are brushed out of the coat.