Other forms: turned over a new leaf; turning over a new leaf; turns over a new leaf
For many people, New Year's resolutions are an opportunity to turn over a new leaf, or start behaving in a new, better, or healthier way.
Turn over a new leaf might sound like it has something to do with trees, but it actually has something to do with books. Sometimes, a piece of paper is called a leaf, especially when it's part of a book. (That's why small, short booklets made of paper are called leaflets.) So when you turn over a new leaf, you're actually turning over a new page. In other words, you're starting a brand-new chapter of your life.