In addition to what Jerry has mentioned, you should also consider that too much, or not enough bathing may contribute to flaky skin. However one of the most common problems, could be that the dog is not getting enough omega 3's in it's diet. Please check out the following website.
Besides a possible yeast infection, this website will discuss some of the other commom problems of dry skin.
Some breeds are more prone to skin problems... for instance West Highland Terriers and Boston Terriers. Check into your dogs specific breed health issues...it may help you determine what kind of skin problem your dog has.
It isn't possible to say what would work until the problem is understood. For example, if the dog also has a smell it may be a skin dermatitis or yeast infections. Some breeds seem to be more prone to yeast. If that's the case a medicated treatment that disrupts the yeast infection has to be used. It is possible to get over-the-counter medicated dog shampoo with 1% (I think that's the small level) ketoconazole which can help stop yeast.
Simple dry skin would not have any smell I believe and it my be worth trying a treatment that advertises it is a treatment for that condition. I think soap with "oat meal" is one of the popular skin treating soap. I think many dog shampoos are in fact irritating but I can't give a list of offenders.