As a business that sells vinyl graphics I will tell you what I send to all my customers as far as care of these products.
The short of it, wash with a mild diluted car wash soap, never power wash, dry with microfiber LIGHTLY, and once dry you can use a SILICONE or Teflon Based Polish designed for vehicle graphics.
Here you go:
http://www.digwraps.com/proddetail.php?prod=WrapPolish