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.

It's only FITTING you should look the part.
Game of Thrones Season 1, Episode 6

- A FITTING reward for a hero.
- SAMWELL: Uh, hold on.
Game of Thrones Season 8, Episode 4

It's called FITTING in.
By the way, good luck.
The Big Bang Theory Season 10, Episode 20

It's FITTING...
Westworld Season 2, Episode 10

As a result, I've often felt like an outsider,
never really FITTING in...
The Big Bang Theory Season 1, Episode 10