keep one's nose clean字面上是保持鼻子干净，引伸的意思是“安分守己、不找麻烦、不惹事生非、洁身自好”。

【例句】
Since leaving prison, he's managed to keep his nose clean.
自从出狱以来，他已做到安分守己。

I just moved to the newschool last month, so I was trying to keep my nose clean.
我上个月才刚转到新学校，所以我试着不惹事生非。