From Longman Dictionary of Contemporary Englishkeep your nose cleankeep your nose cleanspokenBEHAVE to make sure you do not get into trouble, or do anything wrong or illegal Sid’s got to keep his nose clean or he’ll end up back in prison. → nose
Examples from the Corpus
keep your nose clean• But keep his nose clean and take their money, and he could have a marvellous life in Berlin.• He's been sentenced to seven years in prison, but he'll be out in four if he keeps his nose clean.• But journalists are supposed to keep their noses clean, or at least tell us when they don't.• It's not a great job, but if you keep your nose clean, you should be promoted by the end of the year. 