I use one tire lever, steel core, to get my tires off. The technique I use is similar to what many others have said. Let the air out and then squeeze the tire into the center of the rim. The next step is the critical one. I hook the tire lever on the tire and lock it down to a spoke. Then I go around the tire the second time squeezing the tire into the rim. The tension seems to hold the tire down into the rim. I am generally able to unhook the tire iron and slide the tire off with the lever.

The first go around breaks the tire out of the bead hook and the second effectively reduces the diameter of the rim mount.