One word folks;
Make yourself a simple mouse macro to babysit your commerces (and contracts if need be) for some easy cash. Think about it; all commerces are ready to collect every three minutes. But who in their right mind is going to watch the commerces like a hawk for longer than say... an hour? Commerces also cost nothing to mantain (such as the signing fee for your contracts) and can be built in much less time than some of the homes and other buildings. But let's get back to one of the most important parts of this issue.
A lot of time is wasted when you are away from the game/computer. Say your stadium makes 40k every 3 minutes. In one hour that single commerce is making 800k. So... what are we losing out on when we sleep? Average hours of sleep are 5-8 hours a night, so let's split the difference and say 7 hours. That's 5.6 MILLION bucks. Later in the game that isn't a ton of money, but remember these numbers are with just 1 commerce. Either way,wou it be great to wake up after a long nights sleep and see the 5.6 million you've earned in your sleep? Now I know some of you are going to say this is cheating. Sure, if that's how you want to look at it. It may seem negative but hell, you spent the money to build the commerces, you're keeping the game going by playing it and the more you build, the more you are apt to drop a couple bucks for millionaire gold so you can reorganize and maximize! I've done it. Still want to get rid of "cheaters"? We help keep the game alive too. So why not give macros a try today and see your city start to flourish!
Also, for those of you who do not know what a macro is, it may be too complicated for you to use this method. Read up about macros and decide for yourself if you are comfortable using. I will also recommend the program "Workspace Macro Pro" simply because it is extremely easy to use and works well. Boss doesn't mind/know if you leave your work pc on at work at night? Throw a macro on overnight or better yet over the weekend and make some bank! Got a laptop or pc at home you can do the same with? Awesome! Don't forget you can log onto facebook from another pc and use the rest of your games, reply to your messages etc without screwing up the game running on the other computer. Just make sure you don't go to the same game at the same time or you are liable to screw things up. Now get out there and have some fun!
By the way, just in typing this and letting my macro run; I've made over 11 million. Word.