First, I let Piper crumple the foil up into a ball, and then I unrolled it and spread it flat on the surface. I actually used the heavy duty foil, but I imagine that regular would work fine too. The thicker type might hold up better and be less likely to rip however.
Next, my little artist painted the foil with its first layer of paint. Note to self: I really need to get some other colors of paint. All of her artwork is starting to look the same. She did the first layer in green and on the second day, did the second layer in purple. You should have some thickness to the paint layers so the next step is most effective.
Finally, after the paint is completely dry you will use the white wax crayon. Lightly rub it over the paint to emphasize the foil wrinkles. Piper helped me do this last step, but I did have to help her quite a bit. I noticed that if there was only one layer of paint, it flaked off easily.