Though I believe that the most effective way to learn English (or any language for that matter) involves a certain amount of in-class training in order for learners not to pick up and reinforce bad habits, it is essential for learners to engage in a good amount of independent study. The following are some important tools and strategies that are worth the time and investment:
- A good English-English dictionary (NOTE: these should be intended for learners)
- A reference & practice grammar guide/book (Follow link for one example)
- A reference & practice book on writing. (Follow link for one example)
- Listen to the news from the BBC and Voice of America on their websites for English language learners.