Do you know that Reading could help you to improve your English. This has been my practice to explore more Vocabulary and to understand Grammar. Because I think learning Grammar from your English teacher or from a text book is sometimes confusing.
Book that I'm talking here is such as Novel, Biography, Classic Books, etc. You can learn how to write properly and how to put word in sentence.
The most helping book to improve your English would Classic Books; Jane Austen's books, Lord of The Flies and others. Why? Because they're consider as one of the best literature and most students have to read it at school for their English class.

Feel free to give some thought about it here and maybe you can tell me your favorite books as well.