I learned a lot from my parents' mistakes. My father made a lot of money when I was younger, but my parents still spent more than they earned, and they were careless with paying bills on time. My siblings and I always had the newest toys, clothes, and gadgets. I learned early on that things do not bring happiness, and they lose their appeal quickly (hedonistic adaptation). I remember thinking how useless all my stuff was at age 10. My father sat me down and taught me the intricacies of credit at age 12, and so I never got into credit card debt, and I set up auto payments and reminders as soon as I had any bills.
However, it took facing the payment of my student loans for me to make the real radical shift in mindset. Previously, I believed my friends, financial aid advisors, and family when they told me that student loan debt was good debt, not something to worry about, something that everyone has, etc. Now, I know that student loan debt is no different than any other kind of debt, and that I have zero tolerance for it. Despite the grind of sending 75% of my take-home pay to my student loans for the next 20 months, I'm glad that I put myself in this situation. Otherwise, I might have taken out a mortgage/bought a car/inflated my lifestyle without realizing what it would feel like to sit under that debt for years. Or worse, I may not have learned to avoid the well-trod lifestyle plan that just doesn't suit me.
I think the best way to teach others is by living your life and answering questions when they arise.