Learn about personal finance and the power of compound interest. Create a budget and start saving for retirement. Contribute to a 401k/IRA/etc. Your goal should be to save 12-15%. If you can't save that much today, start lower, but increase it every 6-12 months and every time you get a pay raise. Save 6 months of expenses for a rainy day fund -- this is especially important in 2020. Pay yourself first. Save for a vacation every year and take it. Travel the world and get a different perspective.
Every year you don't save for retirement means you'll need to work another year, or save even more when you're older (think 20-30% of your salary).
I'm making up for lost time now. I used to buy new cars and toys. I bought my current car 27 years ago; it still runs great.
I wish someone had told me this 30 years ago. I hope I would have listened.