When the animals first chased Jones out, they took a tour of the farm to see what all was there. Part of that tour was a walk through the farmhouse where they saw all the "luxury" of the humans and how they used animals to make items for their pleasure. They also walked through the butchering rooms where they saw the knives used to cut up their comrades to sell for money. They buried the hams (IE: the corpses of their friends).
Seeing as the place had become a place of torture for animals, and a place where humans set themselves up as better than those they led...the animals (led by the pigs) decided to turn the farmhouse into a museum...so they could all remember what life was like under the rule of the tyrant Farmer Jones. There was also a command that went out that no animal would sleep in the beds, nor should any animal consume the human's alchohol or wear their clothes.
As we see, though, as the corruption of the pig-leaders progresses they feel themselves above the law and they start living in the home, drinking the alchohol, and wearing human clothes. Since the theme of the novel is about power corrupting...it seems inevitable that the animals would break all the laws made for the commoners.