Most consequential changes:
1. Tracking spending in detail. Nothing like knowing exactly where the money is going to shame you into reining in extravagance.
2. Whenever cash starts piling up, making a concerted effort to sweep it into the savings account and then the brokerage account instead of finding some indulgence to spend it on.
3. Re-negotiating/shopping around for car insurance and internet/phone service. The monthly savings add up.
4. Learning about and applying retirement calculators that are based on actual spending, actual market history, and can account for actual expected supplemental income (cFiresim and Firecalc), instead of the typical financial advisor's calculators that are based on 80% of final salary and do a poor job accounting for SS, pensions, and market returns. Using these calculators helped me discover that I am much closer to FIRE than I thought I was.
5. Learning more about strategies to tap qualified retirement accounts early and minimize the associated taxes. I was already aware of the 72t rule, but learning about the Roth pipeline and how to combine it with living off of capital gains/dividends to essentially eliminate taxes in FIRE was a really big revelation. I guess this doesn't really count because I'm not implementing it yet, but the knowledge of this strategy definitely played into the FIRE-is-possible realization.
My favorite blog article is probably a tie between Shockingly Simple Math, A Millionaire is Made Ten Bucks at a Time, and When the Back of the Napkin is Worth Millions. I think if MMM had only written those three articles, most of his job would have been done. The other articles contain many useful strategies and details, but those three contain the entire framework for FIRE (FIRE is possible if you save X percent of your income, you can save X percent if you pay attention to the everyday choices you make, and here's how to figure out how close you are to the goal).