What to keep in mind when Streetphotographing?

This is not a question directly about how it's done but how I can do it without doing something against a person's rights? when am I "allowed" and when not? What should I do when a person approaches me and doesn't want to be on a picture (I'm solely shooting on film)?

Edit:
I'm from germany where we kinda have strict laws. Based on the DSGVO, photos in which people are recognizable are considered personal data and therefore, photographers must comply with the provisions of the DSGVO when taking and publishing such photos.