I don't think I've become a lot more hard-working, but definitely more. A few things:

• Finding work I enjoy and which I'm good at. A cliché but probably still underrated. When I'm working on things I find interesting and which I'm good at, I'm noticeably more productive (10–100% more).
• Strangely, I had overly strict work-life boundaries that actually backfired for me earlier in my career. If I thought I had to work post 6 pm to finish something, I'd start to become stressed and would worry about burning out. In fact, when I stopped worrying about that and worked later when I needed to, I became less stressed and more productive. Conversely, I'd feel very guilty about running errands during the day if it cut into my work day. I'm also more relaxed about that, and it hasn't hit my productivity. I still value work-life balance, I'm just more flexible about what that looks like.
• I use RescueTime which gives me actual data on my productivity. It's striking that sometimes when I feel unproductive, I actually wasn't and vice versa. That's helped me notice what works (reducing meetings, bunching meetings together, avoiding unnecessary travel etc.) and what doesn't.
• Being around other (hard-working) people. I'm noticeably more productive when I have a neighbour, especially when they're a colleague. You pick up on their habits and you get some background social accountability (they'd notice if you e.g. wrote long forum comments instead of working).
• Blocking distracting apps. I use Limit and I know people who love Freedom, the paid version.