Once Napoleon's dogs have sent his most dangerous rival packing from the farm, he immediately sets about establishing a dictatorship. To that end, he starts messing around with the Seven Commandments of Animalism, most notably "No animal shall drink alcohol." Napoleon likes the occasional drink or two, and besides, he doesn't want his power to be curtailed by what he sees as petty and restrictive regulations.
He also starts trading with humans in the nearby village to provide funds for the windmill and other improvements on the farm. When Snowball was around, Napoleon was adamantly opposed to the windmill. But with this deadliest rival out of the way, Napoleon can now set about building a windmill and passing it off as his own idea. It will stand as a towering monument to what he believes to be his foresight, vision, and incredible genius.