Your first point of contact when looking for a flat or a room is the Student Services organization at youruniversity. Student Services operate their own halls of residence that offer value-for-money accommodation for students.
They also maintain a file with the addresses of private landlords and landladies. They additionally offer a particularly interesting service for international students: Many Student Services sell Service Sets for foreign students. These sets can be booked via the Internet before you come to Germany.
In general, a Service Set will include accommodation, meals and health insurance. This guarantees that you have a place to live when you arrive in Germany. You can find more information about the Service Sets on the website of the German Association of Student Services Organizations:
The DAAD also offers detailed information on flat-hunting – including tips on rent contracts and on living in shared flats (Wohngemeinschaften) –on its webpages.