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.

Should we say something to him?
The Big Bang Theory Season 10, Episode 5

Maybe we SHOULD pitch it
to Colonel Williams today.
The Big Bang Theory Season 11, Episode 8

then you SHOULD just tell me
what the hell is up.
Breaking Bad Season 4, Episode 5

I SHOULD have thrown you
Game of Thrones Season 4, Episode 9

I SHOULD probably give you
a heads up about his mother.
The Big Bang Theory Season 2, Episode 12