Here's a cool little article that was published in a fan magazine in May 1972. It features some brief quotes from The Partridge Family's makeup artist talking about Susan Dey's routine and her great skin:
While interviewing Mel Berns, Jr. Susan Dey's makeup artist and for that matter, the entire cast's makeup artist on The Partridge Family, Mel had interesting little tid bits to offer all of us.
First he mentioned how important sleep was, but he knew that in this business it was something hard to obtain. With the long hours that our favorite stars put into shooting a series, there really isn't much time for rest.
"Susan has to be on the set about 6:15 in the morning most of the time for makeup and then a daily hair schedule." Mel went on to say, "with a face like Susan's there really isn't too much you have to do -- in fact she is one of the few stars that doesn't wear false eyelashes, she has the kind of skin that makeup just rolls on -- and off."