This GTA 4 money making method is alot different than many others in the fact that it outlines the best way to make money, and its not really what you want to hear. Just do the missions. The missions will provide you with enough money to coast through the game. Its not like you need an astronomical amount of money to function in Grand Theft Auto 4.
If you personally have any tips for making money in Grand Theft Auto 4 please feel free to post them in the comments section.