Requested by @lilydiamond, presumably because I am a self-taught polyglot. Well, I did start out bilingual (English and French). And I was taught Tamil and German in school, but do not speak either very well. I did teach myself Italian and Spanish, in which I am fluent. Which is why I believe Self-Taught is your best shot at becoming a polyglot.
  1. Being raised bilingual helps. If you only speak one language, you are so identified with it your brain doesn't even realize it's just a system. As soon as you add a second, you give your brain the ability to analyze, understand and learn any other. So once you are bilingual, you've mastered the biggest learning curve towards becoming a polyglot.
  2. Don't bother with regular language classes. How many of you took years of these in school and barely speak a word today? If you have kids, send them to a bilingual school. Or enroll them in a language immersion program. The latter goes for you too. You can't just be "learning" a language. What use is that? You have to operate in that language.
  3. Start from the source. Visit the country whose language you wish to learn. Listen to people talk. Read everything. Go to the movies. Pay attention to body language and intonations. If you can't travel, listen to Internet radio in that language. Watch films - without subtitles. Language isn't just about words. It's a whole world view.
  4. Just try it! Talk - no matter how little vocabulary you know, or how broken your sentences, or how terrible you think your accent is. As a teenager, I would read Italian out loud from my best friend's magazines, not understanding anything I was saying, and she would ridicule me. Today, I speak and write Italian fluently. Joke's
  5. Make it up as you go. Granted, I had an advantage with Italian: I'm French. I would just use French words and add vowels at the end, and hope to get lucky. Sometimes I did, a lot of the time I didn't. Both outcomes were useful. I eventually whittled my way down to pure Italian. And my interlocutors and/or I got a laugh out of it.
  6. Read. Even if you understand next to nothing. Start with kids' books - the pictures help. I learned a lot of words from context. I looked up very few words in the dictionary - its laborious and boring, like you're studying, not learning for the fun of it. I let myself read without understanding every word - eventually it pieces itself together.
  7. Once you've established an "organic," at least rudimentary understanding and ability to communicate, THEN you may take classes to ground vocabulary, grammar and verb tenses. This is how we learn our mother tongues - first in their "real" contexts. Then in a classroom.
  8. Nota Bene: Starting the other way around is not fun and lacks the meaning that will make that language something more innate than acquired - and therefore better engrained and not as easily forgotten.
  9. PS: Pick one language at a time. I toyed with Italian and Spanish simultaneously for years, and never progressed passed the basics. As soon as I focused on one, both got better.