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.

Briefly.
Game of Thrones Season 3, Episode 1

I BRIEFLY considered
that I had a brain parasite.
The Big Bang Theory Season 8, Episode 8

However BRIEFLY.
The Big Bang Theory Season 1, Episode 1

he came by to re-establish contact
with me. We caught up BRIEFLY.
Breaking Bad Season 4, Episode 8

Briefly. Very, very BRIEFLY.
Breaking Bad Season 5, Episode 11