keep your nose clean

Meaning: 
If you keep your nose clean, you stay out of trouble by making sure you don’t do anything wrong.
For example:
Our son Michael is in trouble with the police again. I really wish he’d learn to keep his nose clean
It’s important for sport’s stars to keep their noses clean because they make a lot of money for endorsing products, and     they could lose this income if they got into trouble with the law.