If you are a developer start creating small things. Don't go jump into a large web app. Small bites will help motivate and create a momentum so you can start doing bigger things.
For example, last year I created a couple of jQuery premium plugins, I putted a price tag on them and offer user support. Some of people said "no way, your plugin will make it, there will be free version of it anytime soon".
Guess what ? Almost one year has passed, there aren't any full featured alternatives and I'm making a $xx bucks on a daily basis. I'm not making $50, but it's close tho. For the effort I've put into it I pretty happy with the outcome. Clients appreciate the fact that I offer support, and the best thing is, I haven't yet give any support because none of my clients have request it so far.
In a nutshell, my best advice for you is:
- Start by doing small quality things.
- Create a solid client base, keep them happy and show them what you are doing currently
Soon enough your will start see some profit.