The way it happened is that I was already working on my Iridium Flares app, when one day I saw a certain new app launched. I knew I could do it better and I already had some useful code from another project, so I called in sick from work for one day, and hacked out a better version of what this guy had just launched. That app's user reviews told me exactly what to build. It took off from there.

I have built several Android apps in the early days of Android. The just-mentioned app, which was my most profitable one, was selling for $3.95 and netted about $50,000 over the course of its life. Highest monthly income from that was $1500/month for about two months.

I also had an Iridium Flares app for Android. It contributed maybe about 5% of the numbers stated above. This app was priced at $1.95. Both apps had a free version running ads. Most of the revenue came from the paid version of the other app.

In the early days, simply putting an app on the Play Store was enough to have people find you through the search box and the 'new apps' list. I remember I was scanning the list of new apps every few days for neat new things to try on my G1. Making a better mouse trap would ensure your app got installed.

Which brings me to the present: I just launched a cryptocurrency price charts website a few weeks ago with a friend. https://pizzacharts.com Got about $20 in donations at launch. We have a freemium model, $9/month only payable in Bitcoins at the moment, and ads. We'll see what kind of revenue comes out once we scale, fingers crossed.