The answer to that is universal. Living beneath your means. That's the most important financing lesson anyone can learn. Whatever you make live below your means. Everything else comes after that.
I feel like the 5 most important financial rules are:
- Live beneath your means.
- Save and invest most of the difference created by rule 1 as well as extra money you come into, bonuses and job raises.
- Figure out the standard of living you're comfortable with and maintain that as long as possible. Avoid lifestyle creep.
- Never use debt to buy anything that depreciates in value unless you have the cash to comfortably own it outright when you buy it.
- Never pay interest on a credit card.
I learned all that stuff the hard way cause in my 20s I broke all those rules constantly and I was usually broke.

One of the better posts Ive read on any MB.