One Tip I have is to create a (private) Facebook group every semester for outgoing and incoming Erasmus students (and communicate this to all Erasmus students!!!). Outgoing Erasmus students from the Uni Potsdam are looking to subrent their room for 1 semester, wheras incoming Erasmus students are looking to rent a room for 1 semester. In this Facebook group, they can easily find eachother. This system of subrenting rooms by Erasmus students to other Erasmus students worked very well at my previous university!