This is a dialogue I recently overheard at a birthday party:
– I’ll go and buy some cigarettes.
– I thought you’ve turned over a new leaf.
– Who told you that? Maybe I said I was going to smoke less.
Clearly, ‘to turn over a new leaf‘ means to start afresh and/or to kick a bad habit.
More examples from the trusted sources:
– Everyone deserves a chance to turn over a new leaf (The Economist).
– Mr da Silva has tried to convince the market sceptics that their fears are unfounded, that he has turned over a new leaf (The Economist).
– Why not turn over a new leaf as the New Year approaches? (BBC)
– The people will never allow the crimes of the former regime to be repeated in any form because they are looking forward to turning over a new leaf where they can learn from their past mistakes (BBC)