I am covering several tiers in styrofoam and doing it a week in advance. How do I keep my fondant shiny and prevent it from drying out?

Rub your hands with a light coat of shortening. Massage carefully the surface of the fondant, be very gentle, but try to get a uniform and even coat. Let it sit for an hour, since the fondant may absorb some of the fat. Look at it under different types of lights and different angles to be sure to get the kind of shine you are looking for. If the result is too dull, apply another coat of shortening. On the contrary, if the surface is too shiny, use a paper towel to remove the excess. A paper towel also will help if your shine is not even. We used to do it in the bakery with both, dummies and real cakes alike. Hope it helps and good luck!