Travel, live abroad if possible, and experience living in a big, culture-rich city. Unfortunately the economic realities of the 2020s are making this increasingly out of reach for many youth, but if you have the resources and opportunity, absolutely go for it. As you get older, responsibilities and lack of energy will likely sap much of your ability/desire to move around as much (this isn't true for everyone, but it's extremely common). Even if traditional travel is impractical for you, there still exists cheaper opportunities for exploration that are a bit off the beaten path, such as the WWOOF program.
Regardless of your situation/location, one thing that basically anyone can do is get involved in a cause. Find something you're passionate about and throw yourself into it. Make sure it's something that you can do in-person and not virtually... as in, there are local groups you can join for this cause, although if there aren't you can always try making one or forming a local chapter of a larger org. With the right networking you'd be surprised how many other people will join you, especially for causes that involve your local community. This is a great way to meet other people, get to know the issues facing your neighborhood/city better, and learn to navigate your local government/NGOs. Again, as you get older responsibilities/exhaustion can make this sort of thing a lot harder.
don't move to a big city if you've never spent a significant amount of time in one. i don't care how "culture-rich" it is. true, a lot of people love the noise, crowds, crime, stink, traffic, astronomical prices for literally everything, and all the other crap that's tangled up in city life, but there's no amount of money anyone could pay me to put up with even one of those things ever again. if you're in your 20s, maybe you'll love the night life. but that gets old quick. or you better hope it does...
I mean, obviously it's not for everyone, but it's important to actually experience urban living for yourself before deciding you hate cities. Especially given the political situation in the United States right now, where so many suburban and rural residents are bashing cities and urban living without having properly experienced it for themselves; I think there would be a huge bite taken out of the urban/rural divide if more people had experience living in cities, and got to personally see the good and the bad for themselves. Plus your twenties is a great time to learn street smarts, because that way you'll be less likely to have a bad experience when you do visit a big city in the future, whether it's for something fun like a concert or something serious like going to a medical specialist. There are a lot of basic lessons like "never ever leave anything visible in your unattended parked car", how to use public transportation, being able to firmly say "no", and general situational awareness that are just good life skills that city living forces you to pick up.
I'm not at a point in my life where I want to live in a big city anymore, but I'm so, so grateful that I did in my youth.