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.

Well, this certainly is a thrill
for us. Lunch with you two,
The Big Bang Theory Season 12, Episode 13

Go out to LUNCH instead of,
you know, be LUNCH.
The Big Bang Theory Season 10, Episode 20

She's clearly having a working LUNCH
and preferred to eat alone.
The Big Bang Theory Season 10, Episode 24

Want to grab some LUNCH?
The Big Bang Theory Season 11, Episode 11

It's why we invited you
to this LUNCH.
The Big Bang Theory Season 12, Episode 21