D. Things to avoid

• Classes
  Unless it is social company you are after, group classes are a waste of time and money. You should rather buy you good tapes and books and then invest the money you saved by taking private lessons with a native speaker. If you think you are too weak-willed to do it on your own, you'd better stop learning languages right now because you're never going to make it even with classes.
• Bad books
  You can tell a bad language book rather quickly. First, a good standalone book must include some tapes (the more the better, but 8 would be a minimum). If it doesn't, it may still be a useful purchase but you need something else with tapes. Bad books tend to be heavy on grammar rules and low on examples and dialogs. Don't come to tell me that you are from the old school and that that's the way you are used to learn : you can't learn a language by learning dry grammar rules, and you should know it by the time. A bad book usually starts with heavy dialogs with plenty of words you scarcely use, where good books start with the most useful words and phrases (alas, it is small talk).
• Schools
  I have never known in my life somebody who learned a language at school, although I think there are some and it is possible. But if you are young, energic person wishing to learn a language, you should definitely learn it on your own, even if they teach it at school. It's not so much that school teachers are unqualified, but rather that they adress a group of people and that you must follow the heavy tread of the most stupid in the classroom. Also, hours are unsufficient, your brain won't follow the rigid class schedule, and school books are rarely state-of-the-art. Anyway, if some reader has had a positive language learning experience in school, I'd be glad to read it.