...how did you do it? Did you buy a CD/tape? Take a class at a community college?

I worked my ass off. You need to get a series (a SERIES) of really good text books and spend at least a year drilling yourself with vocabulary. And then, you need to immerse yourself in the language by spending time there.

Just beware that in the process you'll destroy your knack for either languages in order to be able to think back and forth between them. There was a time when my English turned total crap (and I consider my English to be very solid), and there was a time when my German turned total crap. But after essentially breaking them both down, I was able to flip the switch, and now I can hold a conversation in English while reading my books in German or vice versa.

Also:

MUSIC! MUSIC MUSIC MUSIC! You get great vocabulary and expressions that way.