Turn over a new leaf
Definition 1 of 1
Pro Tip 1/3Positive Change
Often implies a significant, positive change in behavior or attitude. 
She turned over a new leaf and became more punctual for meetings.
Pro Tip 2/3Self-Initiated
Used when someone decides to make changes themselves, not forced by others. 
He turned over a new leaf and started studying without being reminded.
Pro Tip 3/3New Beginnings
Suggests a fresh start, often after a period of mistakes or undesirable behavior. 
Following her apology, she turned over a new leaf and worked to regain trust.