[Nagareboshi]

It's possible if you're really motivated and determined and have the proper resources. If you want to learn it on your own, I would suggest one of those computer programs that teach foreign languages. If possible, try to take an English class at a college. If you have any friends who can speak English, use it with them. Use English at every possible opportunity. Watch English movies or TV shows, and listen to English music (it helps you to expand your vocabulary).

You seem to have a basic understanding of the language already, so it shouldn't be too difficult for you to improve. English is my native language, so if you ever have any questions, feel free to ask me.