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.

Has the Faith leveled OFFICIAL charges yet?
Game of Thrones Season 6, Episode 3

It's my OFFICIAL NASA portrait.
The Big Bang Theory Season 6, Episode 5

Mrs. Pinkman, I swear to you,
I'm not here on OFFICIAL capacity.
Breaking Bad Season 2, Episode 2

I would like to keep
the OFFICIAL flag of our apartment.
The Big Bang Theory Season 10, Episode 10

It's OFFICIAL. We're never
going to see the Avengers.
The Big Bang Theory Season 12, Episode 20