Visit an English-speaking country for some time

Take a (summer) course in a English-speaking country

Read books, magazines, newspapers in English
http://learnenglishteens.britishcouncil.org/magazine

Good books in English

Watch films in English without subtitles
https://ororo.tv/ru
http://learnenglish.britishcouncil.org/en/listen-and-watch

Surf the Net

Communicate with people who speak English