I'm going to share you stuffs from my experience, or better, how to get to 7 billion in one month max.

So as you know, the first thing you need to do when you join MonopolyCityStreets is to buy a Street. They usually tell you that you can buy a street from your own city, but in most of the time this isn't possible. So start searching for a street.

Be patient, don't rush in your decision and search for a street with a higher value, higher than 1 Million.
Once you choose your street, buy as many small green houses as possible. If you buy a street of 1 Million, and you start buying houses, you'll have 2 advantages:

1.  Next day you'll have a fortune of 2.1 Million
2.  You'll receive many cards which will allow you to protect your streets, maybe even get more money.

So that's about it, share other ideas with us if you want.