turn over a new leaf
“Turn over a new leaf” is an expression that means to correct one’s behavior or attitude; to make a fresh start.
The origin of this idiom began in the 16th century. People referred to pages in books as leaves. “Turning over a new leaf” literally meant to turn to a blank page in a workbook to begin a new lesson. Figuratively, what the expression suggested was that you can change your behavior for the future and begin again as if turning a new page in the book of your life.
Here is the idiom being used in a sentence:
If you haven’t been feeling very healthy, maybe it’s time to turn over a new leaf
and start exercising.