From airport BER to the apartment: 

•  You could take the S-Bahn S9 (subway) or train direct to station S+U Alexanderplatz (35 min.). After that you change to the Tram M4  to Hufelandstr (8 min). 
•  You can take the S-Bahn S9 (subway) to station S Berlin-Schöneweide (15 min), then change S8/S85 to S Greifswalderstr (20 min). After that you change Tram M4 to Hufelandstr. (3 min).
• You can take the S-Bahn S9/S45 (subway) to station S Adlershof (10 min.), then change S8/S85 to S Greifswalder Straße. (24 min) After that you change Tram M4 to Hufelandstr (3 min).

From ZOB to the apartment:

You can take the S-Bahn (subway) from ZOB S-Bahn station Messe Nord/ICC to station S-bahn Greifswalder Str.

Take the Ring-bahn S41, this is the north direction. Get off at S-Bahn Greifswalderstraße. From there, catch the M4 tram, the direction of S Hackescher Markt and get off at Hufelandstraße. 

The apartment is a 1 minute walk away.

 From Hauptbahnhof to the apartment:

 You could take the subway to S-Bahn station Alexanderplatz.

Then you could take the tram M4 from  Alexanderplatz  to Hufelandstr (3 min).

The apartment is a 1 minute walk away.