1. Ask permission for collecting data

2. Keep sensitive data safe

3. Restrict access to said data

4. Keep a log of what happens with the data

5. Delete it upon request

6. Have all of the above documented and adhere to the protocol.

It's such a none issue unless you're relying on the very thing GDPR is designed to combat. If you not collecting and selling peoples data, and you don't do the above already, see this as a good opportunity to do what you should have been doing all along. There is such an awareness now, that it's the easiest it has ever been to know how to handle sensitive data properly.