Say, we're given a simple puzzle to create a project that will generate $2-4k per month. How'd you solve it?
Additional data: you are a developer that can do both backend and frontend web-development and possibly mobile development through tools like phonegap or rhodes framework (although mobile development will take more time).
Ideas?
Or develop a new, unique mobile app (that is more risky than implementing a proven concept on a new platform).
However, be wary of tools like phonegap. Mobile market is very competitive so the quality of the implementation is a big factor in success if there are multiple implementations of the same idea. Pick one platform (either Android or iOS) and go native.
Android, thanks to using Java, is easier to program natively than iOS.
As a bonus, the market for both Android and iOS devs is hot and will grow in near future so as a bonus, you'll be able to convert your experience into well paying job (or contract work).
Coming up with a project that earns $2000-$4000 a month is like relaxing the constraints -- you no longer have to hit a particular flea, you can hit any flea on the hog's back. This is more probable, but it's still awfully difficult and involves a lot of luck.
The best solution is to just keep on firing at that hog, and hope that you hit a flea eventually. Who knows, it might be the billion-dollar one.
Build a badass product but suck at marketing, you probably won't get many users. Build a shit product but have badass marketing, you'll get a ton of users even if they don't stay users in the long run. You need a balance of both. Rather than focus on just the project, figure out ways to market stuff.
It's very prescriptive on exactly how to do that.