It has been quite a while since I touched an Android phone the last time for code projects. I got in contact first time with an Android phone during an open source conference in 2008 in Sydney when I met Chris DiBona (Director of Open Source at Google). Announcing the SDK 1.0. Soon after I got the G1, aka HTC Dream phone which was the first Android phone available. I could not even imagine this platform would be so widespread adopted and pushed in the years to come. I was even thinking about the investment that time, spending a few hundred dollars on a phone that might be just a experiment. In 2010 I also bought the Nexus One.
Anyway I created some apps for personal use, experimented with the apps market but due to other development and work focus lost it out of sight and just remained normal Android user.
Now my interest returned, at least to update my knowledge about this technology. Today things are becoming a bit easier (IDE, documentation) but also more complex, mainly due to the massive range of devices and manufacturers which makes screen design quite challenging, but also to security concerns as more spam and junk apps are around, users are no longer so flexible with the app security settings.
Coding becomes more convenient, now Android got its own IDE, the Android Studio. After an initial download and subsequent additional downloads of required packages you can start with your projects straight away.
With Ubuntu just just download the linux package, make sure you have a JDK installed, and execute the studio.sh shellscript in the bin folder.