What is the best way to attach rice paper to fondant and gumpaste?

If you mean icing sheets or sugar paper, you can use piping gel, water, crisco just to name a few. I mainly use water, but only use crisco when I need it to slide around before setting.

i've used rice paper for my dragon wings (in photos) and i attached them with a tiny bit of water to the fondant covering the dragon. but in retrospect-now i would most definetly use melted chocolate instead. as water made the rice paper transparent and limp. hth

You only need a little bit of water when attaching it to rice paper. but my guess is corn syrup or piping gel may work better in that instance