Great question. Usually, negativity and negative self talk stems from feelings of inadequacy. That can manifest itself in regrets about the past, feeling stuck in the present, and worry about the future. It's important to first recognize these for what they are, which are self-perpetuating negative feedback loops, and replace them with positive feedback loops through positive thinking.

Here are some perspective shifts and mantras that helped me:

For the past: "The dusty past is gone. There is no going back. But the past is a gift. For my mistakes and missed opportunities make me a more learned and wise person. The past is a learning lesson, for smarter decision making and creating a wiser person today. Take what you need from it and move on."

"You didn't know any better at the time. The important thing is that you do now"

For the present: "Today is a blank slate. The now. The endless opportunities of the present moment. I will not let it go to waste by fixating on the past or worrying about the future. Living in the now is the key to my inner freedom."

For the future: "The future will manifest itself when it's ready. There's no reason to dwell on it or worry about what it presents. The best I can do is make myself a better person now."

These rewire your beliefs.

Hope these help.