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.

...to accommodate the duration
of an AVERAGE bowel movement."
The Big Bang Theory Season 1, Episode 4

...that I'm farther along the evolutionary
scale than the AVERAGE human.
The Big Bang Theory Season 2, Episode 5

Well, if we assume
that your looks are AVERAGE...
The Big Bang Theory Season 6, Episode 8

Then using that number as
the AVERAGE speed to calculate
The Big Bang Theory Season 9, Episode 8

...are significantly smaller
than the AVERAGE for someone of my size?
The Big Bang Theory Season 2, Episode 5