- Securing your system (like PCI)
- Training your employees
- Disclosing a data breach in a timely way
AND if the company follows all the rules they are protected from the fines.
There is no reason why a company that does their absolute best to be secure but falls vicim to a zero-day vulnerability should be treated the same way as someone that was willfully negligent like Equifax.
If a company is willfully negligent (Equifax, Uber, and AshleyMadison are notable examples) I think a fine is not enough. Revoking their license to do business needs to be on the table as a maximum penalty in the most egregious cases. I'm talking companies that try to hide the breach from the victims, systematically underspend on security, etc.
Edit: As an aside, as someone who has done a number of startups in a CTO role. Sometimes getting the board and upper management to agree on spending money on security is like pulling teeth. A lot of startups end up getting to a 100,000 users without even thinking about security never mind putting appropriate systems in place. Penalties for neglecting security would give CTOs powerful ammunition to be able to invest in this critical area.