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.

You should PROBABLY go.
The Big Bang Theory Season 7, Episode 10

his Grey's Anatomy online fan group
PROBABLY knows.
The Big Bang Theory Season 10, Episode 4

That one's so uptight, PROBABLY
got a wood chipper for a coochie.
Breaking Bad Season 5, Episode 15

Aye, you're PROBABLY right.
Game of Thrones Season 6, Episode 8

Yeah, I PROBABLY wouldn't.
The Big Bang Theory Season 7, Episode 13