One can do a self test and see how many of these most

commonly used idioms s/he knows:  96 Super Common English Idioms (With Meanings and Pictures) | FluentU English

Keep in mind though.  Do not confuse the ability to comprehend idioms with the ability to use them; these are apples and oranges and the improvement of the latter may take much writing exercise in addition to listening/speaking exercises. 

Here are my my 2 cents:  If one really wants to improve his/her English, he/she should follow Mao's teaching: Nothing is improssible if one takes it seriously.  (I'm not a Mao fan, but we don't want to reject good words based on who said them.)