From the Zoologischer Garten train station, you can take the U9 underground line towards Rathaus Steglitz, and get out out at Walther-Schreiber-Platz. Continue walking in the same direction, and go as far as Ecke Forum Steglitz. Turn right into the Bornstraße, and the next street on your right-hand side is the Büsingstraße.
Arriving at Tegel Airport (travel time to the hotel: approx. 40 minutes):
Take bus no. 109 or X9 in front of the main airport building to Bahnhof Zoologischer Garten, change to the U9 underground line, and continue as described above.