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.

On any LEVEL,
do you think she's hot?
The Big Bang Theory Season 7, Episode 12

to the next LEVEL with
another guy, this was nice.
The Big Bang Theory Season 5, Episode 10

I'm willing to take our relationship
to the next LEVEL.
The Big Bang Theory Season 10, Episode 5

SHELDON: Ugh, I don\'t want the next level.
I like this level.
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SHELDON: Ugh, I don\'t want the next level.
I like this level.
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SHELDON: Ugh, I don't want the next LEVEL.
I like this LEVEL.
The Big Bang Theory Season 4, Episode 5

This is Lieutenant Colonel Castro.
Alert Level 5 has just been declared.
Money Heist Season 3, Episode 2