* turn off all the telemetry, crash reports, and sharing of diagnostic information that you can, everywhere you can (apps, OS, browsers, etc.). If you run Windows 10, good luck
* whenever a field says "optional", don't fill it in. This goes for paper as well as virtual. Never share full SSNs, no matter what the form says.
* opt out of all the data sharing you can do and get off all the lists you can - whether Internet-based, phone call, or even letters. Budget time to periodically do this
* get free email addresses and give those out if you have to register. Give out your crappy VoIP number that you don't need and give that out if you have to. It's better than a fake number because it's actually yours (and some losers out there actually use a phone number like a unique identifier)
There's a lot more that can be done, but this is the absolute minimum and you don't have to be technically savvy to do these things. You may still lose the information that you had no choice in sharing, but at least they can't lose what they never had. Regardless of what you do, privacy is dead and has been for a long time. If you want any chance at that, you're going to have to do things like use Tor/Tails (and keep in mind that there are significant functionality trade offs when you go down that road). Ironically, this starts to get into Mr. Robot territory.
And speaking of irony, yes I do realize that in posting this I violated my own rule. But I guess it's worth taking the hit if anyone is inspired.
"Card readers? We don't need no stinking card readers." -- Peter da Silva (at the National Academy of Sciencies, 1965, in a particularly vivid fantasy)