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.

...and engage in CASUAL physical contact...
The Big Bang Theory Season 6, Episode 1

Right. Whereas Jewish mothers take
a CASUAL la-di-da approach to their sons.
The Big Bang Theory Season 4, Episode 23

Of course, the CASUAL mention
of a Dothraki horde,
Game of Thrones Season 7, Episode 2

I've extended a friendly,
CASUAL greeting.
The Big Bang Theory Season 3, Episode 10

Well, it's very CASUAL. No dress code or...
The Big Bang Theory Season 2, Episode 10