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.

are fighting for the same SIDE,
Game of Thrones Season 7, Episode 1

They were born on the wrong SIDE of the Wall.
Game of Thrones Season 5, Episode 1

All his bannermen have rallied to his SIDE.
They'll keep him safe.
Game of Thrones Season 1, Episode 9

On the left SIDE
and on the right SIDE too.
Money Heist Season 1, Episode 13

Yet your brother has chosen
to SIDE with the cockless.
Game of Thrones Season 7, Episode 7