Boardwalk and Park Place are highly overrated. Forget about them.
Own all the railroads. Try to get them at a low price, but if you have to buy one from someone, spend as much as you need; it will pay off in the end.
Waterworks and Electric Company do not bring in money.
Try to own at least one of every color. That way, more deals will be with you.
Try to own the entire side between Jail and Free Parking. There are two cards that tell you to land on St. James Place and New York Ave. Also, they are cheap to buy, cheap to build, but have a devastating payoff with hotels.
Own houses instead of hotels. There are only thirty two houses. If you own two different color sets and build houses, you will use twenty four houses just with them.
Late in the game, you will want to go to jail. You can just sit there and bank in the cash. Early in the game, avoid jail to buy your properties.
If the CPU owns two of the three properties of a color, and there is an auction for the last, raise the stakes high. The CPU will want it.
If you are in an auction, always go $1 higher than the highest bidder.