1. Never give out any sensitive data (age, Social Security Number, bank account informations, credit/debit card informations, legal name, gender, home address, political views, sexual orientation, religious beliefs, login info, and other stuff that can identify you) to websites and services you do not trust and do not have a data officer/a privacy policy.
2. Read the Terms and Conditions.
3. Do not put data on unsecured public servers.
4. Try to store sensitive data on servers not connected to the internet.
5. Change your password regularly, and put special characters in it.
6. enable 2FA everywhere you can
7. if you have to store data online, protect it by using cryptographic methods.
8. try to not link a person to it's data, create an unique token for each person's data
9. use a VPN or a proxy
10. be sure to closely monitor who can access the data. create different levels of permissions. don't allow people to see more than what they need.
and i thinks that covers it pretty much. i'm sure there's a thousand of other things you can do.