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.

I heard you had
some kind of a MENTAL break?
Westworld Season 3, Episode 8

Then as a MENTAL exercise,
I invite you to figure out...
The Big Bang Theory Season 4, Episode 22

And with that MENTAL picture,
I think we're done for the evening.
The Big Bang Theory Season 4, Episode 4

Well, clearly MENTAL tasks are not enough.
The Big Bang Theory Season 10, Episode 22

...of arm wrestling with the MENTAL agility
of Tetris into the ultimate sport.
The Big Bang Theory Season 1, Episode 16