My first suggestion would be to get every account in a password manager like 1Password. In addition to the obvious security benefits, this creates a record of where all your accounts are. For the average person it'll take time for them to remember everything (and they'll realize ones they forgot) - having a place for it all to get documented is the first step.
Once you have that, the next step is to go through every account and close the ones you don't need. After that, go into the ones you do need and modify the settings to disable as much of the tracking as possible.
I'd also suggest people sign up for deleteme: https://joindeleteme.com/ since these public data collectors can't be stopped without continued effort and I don't think there will be laws to stop them anytime soon.
For more technical users, I'd suggest they get their own domain and use fastmail with aliased emails for each account - but realistically regular people will not do that.
There are also advantages to having a public presence online (both professional and personal) - the issue isn't so much that you need to be 100% dark, it's that your public presence should be under your own control. One of the reasons I'm excited about Urbit is because it has the potential to give this control back in a way that could actually work.
I think culturally we also need to be more understanding of people making mistakes as the grow up and saying stupid things as they learn, but that's somewhat of an orthogonal issue so I'll leave it there.