Last summer I bought a cheap ($8) pair of sneakers to dye. I had tried ice dying a few tshirts and wanted to try a pair of shoes.
Wet shoes throughly.
Rub Vaseline on the rubber sides of your shoes. If you skip this step, the white rubber sides will absorb the dye.
Make an ice dam around your shoes to hold the ice in.
Cover shoes with lots and lots of ice.
Sprinkle powder dye over shoes.