Languages are my thing. I am a Spanish teacher. Majored in both Spanish and Russian, have studied French, German, Japanese, Esperanto, maybe another can't think of right now, plus having studied a lot more informally (just from a book). I have taught Spanish to adults too, which in many ways can be more enjoyable than teaching high school students.

I always recommend taking a class if at all possible, but if not available go with a computer-assisted program, maybe even something online. Also the best thing to do is find a native language tutor (could be online also) to assist you in your studies. The best thing for me in learning languages was being forced to write (communicate thoughts) and of course living with host families in Spain and Costa Rica. I'm fluent in Spanish, passable in French, and barely functioning in the others, despite having lived in Japan for a year. The languages tend to fade away, yet I find if I crack open the textbooks, it all comes back pretty quickly.