Once advertising companies like Facebook or Google reach a certain size, they should be required to pay taxes where the ads are shown to users.
Make a set of basic EU user terms and privacy policy for advertising companies masked as social networks, search engines, email providers etc, some of it mandatory, some of it that they can opt out off. But advertising companies above a certain size shouldn't be allowed to set their own (American) terms.
And please, split up these behemoths. It's not good for anyone that one search engine and one social network rules it all. They have EU-wide market shares above 90 percent. We would never allow that in industries as automobiles or television. We would never allow it for newspapers or tv stations. Somehow, we allow it for social networks and search engines.