Basically you cut the skin free around the neck and hooves with the deer hanging by it's neck.
Free the skin a few inches below your cut. Take a rock or golfball and place it inside the loose skin and push out so you can clearly see the imprint of the ball/rock in the hids. Tie a rope around that pushed out piece of hide with the ball/rock still in it. Make sure your knot is tight.
Tie the other end of the rope to a truck/4-wheeler/tractor. Slowly drive forward and the deer will pretty much skin itself.
NOTE: Make sure whatever the deer is hanging from is strong enough to withstand the pull!!!
Here are some videos demonstrating different variation on the theme:
Video 1
Video 2
Video 3
#3 is probably a bit faster than I would do it, but it seems to work fine for them.
Here's a website that explains it all step by step really well with pics.