Ask HN: What's the best way of learning a foreign language on your own?

Amidst all of these news from Japan, an old itch of mine has re-surfaced: learning japanese. However, I live in a spanish speaking country, and can't find (decent or not) teachers of that language in my town. I've attempted to learn it online before, but haven't succeeded, mostly because I had no guidelines on how to attack this problem. I'm sure some of the HN members have faced this same issue before (perhaps with another language), so I'm asking: If you learnt the language (be that japanese or other) on your own, how did you accomplished it? Which would be the main tips to succeed in this enterprise?