I starting learning in high school because we were forced to choose a language and I was sort of interested in Japanese stuff.
Then when I came to Japan I started getting tuition from a friend (actually it was language exchange as I helped her too).
I have tried some book/CD combination and they were OK.. but they tend to teach Japanese that is not usually used much.. but it isn't a bad way to start.
Living here and listening to day to day conversations sure helps us improve quick!