Use a gentle shampoo.

Dry hair needs a gentle, acidic cleanser. The ideal shampoos for dry hair have a pH of between 4.5 and 6.7, but here's a good rule of thumb: Don't use any hair cleanser that you wouldn't put on your face. Some people recommend baby shampoos, but their pH is usually far too high; such alkaline shampoos dry out the hair. Acidic shampoos are better for your hair.