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.

That is a very strange CUSTOM.
Game of Thrones Season 3, Episode 9

Has the CUSTOM changed
since I've been gone?
Game of Thrones Season 6, Episode 2

Of course I do. The essence of the CUSTOM
is that I now have to go and purchase...
The Big Bang Theory Season 2, Episode 11

Is the CUSTOM different in Naath?
Game of Thrones Season 7, Episode 4

That was his CUSTOM.
Game of Thrones Season 2, Episode 7