There was a point in life when I was pretty good at Spanish. Then, I didn't speak it for years, and last year I went to Puerto Rico. I realized how rusty I was, very quickly. My method, honestly though was essentially just to go try to befriend some locals and talk with them, explaining I'm trying to improve. Obviously, that's not always a very accessible option; but, if possible, talk to a native language speaker!

If I had a kindle or something of the sort, however, I'd love to use it in this fashion in my free time. I would really love to learn as many languages as possible :)