Study on job interview or work on small side project for more income?

[advice_seeker]

If I want to earn more income in addition to my main job, should I study on job interview questions to companies such as google, amazon, etc. in the hope of getting a job there with a higher salary (i know it's extremely difficult...), or should I be a one-man team and spend the time to work on some small side projects such as mobile or web apps, knowing that it'll take lots of time, research, learning, trial and error, no guarantee on any kind of significant income stream...what would you do? Any recommendation or advice?

[sixtofour]

Door number two is more likely to lead to door number three.