When you use the game and get the arrived trains. Get the train that arrives at the station and close the game and double tap the home button and hold the monopoly app until it jiggles and shows the red cursor comes up, then push it. After that re-open and go to the station and get your cash or gold again and again.
Fill all your hotels with thimble rooms as you recieve 125 dollars every 45 mins the rooms are very small I have roughly 58 thimble rooms and I get roughly 10,000 every 45 minutes. Try it you wont be dissapointed