Put yourself in situations where you must listen / write / speak well. It is easy to watch movies and listen to songs without attempting to fully comprehend everything that is being said. Challenge yourself to write a perfect diary entry or review or essay, then have it reviewed. Record yourself speaking, e.g. write a speech and then read it aloud or shadow someone else's. Do listening tests, or listen to podcasts and genuinely try to understand everything. And of course if the option is there, have conversations with native speakers. It is easy to focus on what you are comfortable with (vocabulary and reading) but it doesn't yield the greatest improvement.