And besides, a game of Monopoly among smart, experienced players usually takes between 60 and 90 minutes. Yes, you read that right. Games among “amateur” players often extend far longer for a variety of reasons:
People wait too long to trade monopolies. There’s a train of thought that once you give someone a monopoly, you’ve given them the game. But trading someone the last piece of their monopoly for cash or other valuable assets that could lead to your own monopoly is not such a bad move, especially if you leave your opponent without a lot of money to build up their new monopoly.
People wait too long to build up monopolies. Once you get a monopoly, you should usually build it up as quickly as possible with any spare cash, even mortgaging any unessential properties to increase your purchasing power. This is especially important if you can get to the coveted three-house level, where rent really skyrockets.
--Jim Pagels, Slate, on optimal Monopoly strategy