What’s the number one thing you could have done in your 20- early 30s you wish you did now towards retirement?

Respectfully wanted to know what to do with investing my money in early youth. I’m currently not doing too bad and investing money in stocks and saving. I’m at the point to find new investments or decisions to get me to the next level above the middle class. What could have been done differently and how you now making a profit in your 40s and beyond now? What tips and advice would you give your younger self to others to improve their life for early retirement / set for life?