Pretty straight forward - slit up the inside of the hind legs just as you would casing, then slit from the taint up to the chin, then down each of the front legs. How you stretch it and then trim the superfluous belly/neck hide is what will make the difference in how well it wants to lay flat. Personally, I would not cut the head or limbs off of the carcass before skinning, as having the limbs will make life a lot easier. Cutting them off will leave you skinning a football - which oddly enough, will look a lot like a monkey trying to do something else with a football...