First of all, not many people who play
Crime City, put very much focus into monetizing their 'hoods and coin farming, but doing a little bit of coin farming can earn you huge monetary bonuses. Buildings are cheap, and buying the right buildings can earn you huge amounts of extra dough.
The single best coin-farming building to buy is the basketball court, which takes up 4 times the space of a house or a laundromat, but earns you 315 coins every 24 hours, and costs just 260 coins and 1 steel to build. Build multiple basketball courts, and upgrade them for cheap (upgrading a building increases its earnings potential by half the amount of coins that it earned you to begin with - for example, upgrading a building that earns you 10 coins, will cause it to earn you 15 coins - upgrading it again will earn you 20 coins, and upgrading it again, 25 coins - etc). Upgrading one basketball court 3 times causes it to earn you 787 coins every 24 hours. Upgrading it 4 times causes it to earn you 945 coins every 24 hours.

If you need to make room for even more basketball courts, go to your store, go to "eraser", click "buy", and then erase as many roads as you need to erase to make room for building basketball courts in close proximity to each other. You don't need roads at all - they are just for decoration, and erasing them lets you build more buildings, coin farm effectively, and overall earn more money.
When you level up, you can use your allotted points to increase either energy, attack or defense. Use about 90% of them on energy, as energy is the most important asset in the game as it allows you to do that much more jobs. Increase energy as much as possible.
Follow the goals on the left side of the page in order to know which jobs to do when, and in what order to do them. Following goals maximizes how much money you make for the energy, as more goals completed earns you more bonus money and experience. When you're in an area, any job location with a green arrow pointed at it is one that counts toward your immediate job goal.
Take advantage of free gifts from defeated opponents as much as possible, especially strong ones. Fight tough area bosses (I.E. Big Daddy Remi) over and over to increase your chances of winning free weapons and armor (Remi especially has some strong loot, such as Remi's Little Friend and Remi's Beret).
And very importantly, and this is where all of the extra coin-farming cash comes in, buy as many different types of weapons and armor as possible. Each one your purchase will increase your attack and defense by the applicable amount, as well as your total of weapons and armor owned. Buying more than one of the same kind of weapon or armor, though, will do absolutely nothing for you.
Hope this helps. Thanks for reading.