In school i had good grades in russian, ukrainian and english, despite skipping school a lot. Even now i do not know a single grammar rule of those languages.
What i do is read a lot, including books - russian, ukrainian, english. Last book i read was 'Vampire Lestat', and before it - 'Interview with the Vampire'. I also liked books, translated from japanese to english, - 'Spice and Wolf' and 'Vampire Hunter D'.
I think that reading improves my language skills a lot, without the need to know grammar rules. Also there are a plenty of expressions that do not follow rules.
To learn the proper spelling i watch movies and games with english voice and subtitles.
I am not sure about how efficient these methods are, but at least they work and are free.