Operating systems and applications can always be reinstalled, but your data is unique, making it the most important thing on your computer or network to protect.
Set permissions on the data files and folders.
Some data is confidential; not only do you not want to lose it, you don’t want others to even view it without authorisation.
Use removable storage for the most sensitive data (such as database and key files for password managers)
Use file encryption
Use disk encryption
Assume data loss is inevitable. It’s not a matter of if, it is a matter of when. You best protect your data with a solid backup strategy.
Make a backup of your entire system or synchronise files with a remote system
If you make a backup of a system for the first time to be able to restore a system from (the whole point of it), test it with an actual restore. Having done so helps in staying calm when the **** hits the fan.
You may wish to shred and delete data and not have it found by anyone.
Keep your authentication data in a password manager (on a local usb stick)