gently gently apply the brakes. Don't drive around with the radio on (loudly) because you need to hear the road noises, it will help you know when the car is sliding. If you know that you're sliding forward (not swerving) then let off the brakes and gently reapply until you're slowing down without sliding.
If the rearend starts to slide out. Don't touch the brakes unless the car is pointed forward otherwise the rear brakes lock first and you won't be able to catch it. Like the others said, immediately turn the wheel left if the rear end slides left. The amount you turn the wheel will depend on how quickly and far the rearend comes out. If you know there is definately ice on the road you're driving on, just crawl along in first gear very slowly like you're waiting for a parking place in a car park. If the rearend swings out at these speeds, you should easily be able to catch it by counter steering.
If you're able, find a deserted snowy/icy car park and practice far away from any potential obstacles. Purposely force the rearend out by turning the wheel sharply and hitting the brakes. And practice re-gaining control of the vehicle. But you should still take caution and be very careful. You shouldn't drive over 10mph max on ice. You should be able to re-gain control at these speeds.
If you have ABS, you're at a huge advantage.
Another option is weather chains or snow tyres. These will provide good traction in the snow/ice.