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.

How is it inappropriate for me
to ask it ONCE?
The Big Bang Theory Season 2, Episode 10

- Once again, unbelievable.
- Yeah. Once again, I know.
The Big Bang Theory Season 6, Episode 4

I had that one for five years
and I only had to charge it ONCE.
Money Heist Season 3, Episode 4

Which he only did ONCE.
The Big Bang Theory Season 10, Episode 24

Once you said, "Family is what lives on.
Game of Thrones Season 4, Episode 6