One of the most pleasurable ways to develop your vocabulary is to read poetry. A short poem can give you something interesting to think about and you can see different ways to describe things, people and feelings than you might have thought.
A poem can be read on a short commute, in line at the post office or, well, anywhere. There are some great resources on the internet. You can also listen to poetry on the internet, too.
If you have any other ideas, leave them in the comments, please.