[yk]

In my experience, the most useful thing to learn anything are projects. So you should pick something, for Android, Python, RoR perhaps a stupid fantasy football game ( or some unified HN and reddit aggregator) and solve the problems that pop up while building it. This has two benefits, first you learn about the type of problems that are actually important and second you can truthfully tell a future employer: "I can build stuff like this." and let them decide if they hire you.

(This is likely not the answer you were looking for, but the only skill that you can learn just by reading is reading.)