be discreet in one’s words and deeds;mind (/be on) one’s P’s and Q’s;( )speak and act cautiously
❍ 朋友们都劝他要～，以免再犯错误。All his friends advised him to mind his P’s and Q’s lest he should commit more mistakes.
谨言慎行jǐn yán shèn xínɡ
指说话、办事十分小心谨慎。speak and act cautiously, be prudent, be discreet in word and deed