All of us, that is, users of Facebook and its properties (Instagram, Whatsapp, etc...) should be carefully watching how Facebook handles the Cambridge Analytica debacle. Me? My finger is hovering over the delete button while we learn the full extent of the situation.
In the mean time here's some info from the EFF on locking down your data sharing to third parties and another from Boing Boing on how to really, truly delete your Facebook account. Thanks to the EU and GDPR they actually have to delete it...and some other resources to help you get caught up.

Change your settings via the EFF: https://www.eff.org/deeplinks/2018/03/how-change-your-facebook-settings-opt-out-platform-api-sharing

Audit the 3rd party apps in your account: http://boffosocko.com/2018/03/19/facebook-app-purge/

Delete your account via Boing Boing: https://boingboing.net/2018/03/20/how-to-permanently-delete-your.html

News about the whole thing:

Ars Technica: https://arstechnica.com/tech-policy/2018/03/facebooks-cambridge-analytica-scandal-explained/

Washingotn Post: https://www.washingtonpost.com/news/the-switch/wp/2018/03/20/ftc-opens-investigation-into-facebook-after-cambridge-analytica-scrapes-millions-of-users-personal-information

BBC: http://www.bbc.com/news/technology-43465968