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.

Yes, perhaps we could be of ASSISTANCE
in some current venture.
Game of Thrones Season 7, Episode 4

These men from the capital
requested our ASSISTANCE.
Game of Thrones Season 2, Episode 3

and I could use your ASSISTANCE
in helping me select the perfect gift.
The Big Bang Theory Season 9, Episode 11

Leonard, I could use
your ASSISTANCE.
The Big Bang Theory Season 7, Episode 21

You're asking for my ASSISTANCE.
The Big Bang Theory Season 2, Episode 18