Don't post on social media, especially under your real name.
This includes posting when you'll be out of the house (I.e. vacation), or the details/names of family members.
Run an adblocker with strict tracker protection on every device you use, and opt for the web version of a product, rather than an app.
Use aliases and throwaway email addresses to anything that requires an account. If they end up being something you use, and are required to provide real information, move forward with caution.
Really, though, the worst thing you can do is post on social media.
Big change for me was stop using "name.lastname@email.com", I was giving that info to so many random ass websites and app and services. Just create another email and connect that with your "main" one, that's trivial to do with gmail.
Search for your name on images and see if anything comes up. If yes, try to clean that up. It's usually profile pictures in services.
Don't leave your strava profile public. It's crazy to me that people do that. I don't want even my friends knowing where and when I exercised.
On the same topic, make sure your facebook photos and connections aren't visible to non-friends. It's insane the amount of people who just put everything out there for anyone to see.
Use Facebook as little as possible, but it's ok to be on there I think, if it's needed to stay on touch with people.
Disable location for most apps
Use AdBlock and a cookie blocker
Use DDG or something else then Google for search
Use different usernames on different sites
Don't dox yourself
Use at least two emails, one primary and one you give away to get random deals or whatever else. Let all the emails here go to a folder that is automatically marked as read, just so you can check it when you want to
I created a new Reddit user every year or so, but that might be too far for some.
Use a password manager, a spam email address, uBlock, pay attention to app permissions... Don't rely on algorithms shaping what you see from the world and confining you in a filter bubble. Have some secrets you don't share with everyone. Be aware of things and learn about the platforms and software you use often, and what they do behind the scenes. Also be aware of alternatives and free and open-source software. Don't give away your identifiers to everyone (phone number for sign-up, credit card number, real name and address, ...)
More security than privacy, but does provide some:
Freeze your credit report sharing with all major consumer reporting agencies when not applying for new credit. Without reports, lenders won’t grant new lines of credit in your name. It’s free and timely, as required by US law.
Credit monitoring companies just run credit checks, which they can’t do with your credit frozen. Check your credit every 3-4 months yourself at annualcreditreport.com (proof of legitimacy).
I use Facebook for some hobby groups, and I only use Safari to view it.. the other day my daughter and I were watching The Fast and the Furious movie and I started getting my feed full of all the cars from the movie.. so we did some experiments saying words like KFC and beer while the screen was opened, and we started getting beer and KFC ads in the feed.. i dont know if the app makes it worse, but it was certainly a bit of an eye opener
iPhone unlocked with Facebook opened in the safari browser (no meta apps installed, and the only two apps approved to user the microphone in the security settings are Teams and my Banking app for voice security prompt). We were watching Fast and the Furious on the TV in the loungeroom and we were noticing videos pop up on Facebook on the phone for Honda Civics, then Toyota Supras etc. We then started joking talking about KFC and beer as a test, and within 10 minutes we successfully started seeing ads for Beer, KFC. We then tried another when we started talking about Bryan Adams tickets, and sure enough, we got an ad to buy tickets to Bryan Adams. It would take about 10mins from talking about a topic to things about that topic to start appearing in the feed