Ruby and particularly Ruby on Rails seem to be particularly exciting for people who have just escaped the world of Java. Plus, web apps are the sort of thing where you can make a simple one and entertain yourself quickly. Just find a neat one day project and dive in.

The best way to learn is just to promise a couple close friends that you are going to make a particular thing in the next day or two, and then you will be forced to actually do it. You can get any information you need from the internet.