The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

the head of the baker WHO makes my bread,
Game of Thrones Season 1, Episode 10

That is WHO we have always been.
Game of Thrones Season 2, Episode 2

Who is important enough to Littlefinger
Game of Thrones Season 3, Episode 4

I'm serious.
Who wants to do all that stuff?
The Big Bang Theory Season 7, Episode 14