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.

Fighting for a winning cause
is far more REWARDING.
Game of Thrones Season 3, Episode 3

That's too bad. But still, working with kids,
it must be REWARDING.
The Big Bang Theory Season 6, Episode 22

lf ever you're interested
in REWARDING part-time work,
Breaking Bad Season 4, Episode 7

Oh, tiring, but super REWARDING.
The Big Bang Theory Season 11, Episode 17