The common recommendation is to turn off the exhaust brake, but that's my best friend on slippery roads. By using the rear wheels to slow down your coach, you can maintain steering. If you use your service brakes, most of the braking force is applied to the front which may cause the front wheels to loose traction. At that point you are just going along for the ride and are no longer in control.
If you feel the rear end loosing traction (it starts going to one side) slightly press on the accelerator to straighten the coach out, and try again.
I learned to drive on ice and snow by driving on a frozen lake. It was one of the better lessons my dad gave me as a young driver.