Take your tools and the garment to a sink, or use some other bowl or container of appropriate size.
Take out two ice cubes. I like to use the old-fashioned ice cube trays because they produce ice with a flat top and a flat bottom, but any ice will do! Use a bowl to contain the ice and garment if you can't stack the ice - see below.
Place one cube under the gummed area, with as few layers of fabric as possible (ie - in the pant leg).
Situate the gum spot in the center of the cube, and carefully balance the second cube on top.
For oddly shaped ice: If you're using weirdly shaped ice cubes, place the ice cubes inside the garment and then press it down into a small bowl and put more ice on top.
Wait for at least 30 minutes. You want the gum to get good and cold, through and through.