As soon as possible after your arrival, you should get in touch with the international office of the university and the advisors for international and social affairs at the Studierendenwerk.
They often have useful tips and can support you with help and advice. Many universities offer orientation days for international students where administrative aspects can be done together. They also give a general guide to the university and its facilities.
In many places, tutors in student accommodation, or sometimes mentors from the Studierendenwerk, are available to help international students. Their function varies from Studierendenwerk to Studierendenwerk and sometimes contain the welcoming of new international students in the student accomodation. Mostly, the tutors are the point of contact for international students in student accomodation, but also sometimes for all residents in the house. Is there a tutor resident in your student accommodation? If so, you should get in touch with him/her, too.
A good point of contact for students is the AStA (student parliament) or the StuRa (student council). Students have the opportunity to voice their interests via this politically oriented board of higher education. The AStA/StuRa also offers help and advice in several areas. There is often a contact person especially for international students.
The services of the AStA/StuRa differ from university to university; apart from social and legal advice they also offer cultural activities and cheap learning aids.