What worked for me is simply reading interesting things. You need an intermediate level of proficiency before that. Unfortunately, the language this works best for is English because e.g. if you want to learn about something on Wikipedia, the English article usually contains more info than the others.

This was a problem when I was learning German, I could hardly find anything interesting I could not find three times as much interesting material about in English. Unfortunately I am not much interested in poetry or literature, if I was it would have been much easier. I ended up with fairly desperate choices like 50 Cents autobio in German (Dealer, Rapper, Millionär), which was at least fun because of the complete weirdness of expressing one culture in the language of another.

You probably need to find something that you find interesting and the best sources are in Mandarin. History of gung fu?