Soon there are European elections. Voting for the Pirate parties and getting other people to vote for them is a good way to stop this. They are fighting hard against this law. Especially Patrick Patrick Breyer of the German one. Anja Hirschel, who will follow him, will likely continue with the same vigor.
Donations are also a great way to support. Donate to the Pirates, EDRI, or local groups opposing this.
With the German Pirate Party loosing its seat a strong voice against surveilance is lost.
They also supplied NGOs with information directly from the legislative process, allowing them to act faster (and sometimes you have to be very fast to comment on minor changes with great effect) I hope somebody else at least partly takes on this role.