Take the train line S9, the main airport line, from Schonefeld station into central Berlin, to Friedrichstrasse station. The nearest station to the Hilton is Stadtmitte, and that is 2 stops down the U6 U-Bahn line from Friedrichstrasse. You can either make this change at Friedrichstr., or if you have no heavy luggage you can leave at Friedrichstrasse station and walk south about 8 blocks down Friedrichstrasse itself (the U6 runs underneath this street). The Hilton will be off to your left before you get as far as Stadtmitte station.
One standard fare will take you from the airport to any of these stations in the city. If you are going to be there for a while one of the multi-day passes you can buy from the ticket machine at Schonefeld station is not only good value, but means you can just jump on and off city trains (S-Bahn), Underground (U-Bahn) and buses as you wish.
S/U-Bahn map here :
http://www.vbbonline.de/download/pdf.../su_berlin.pdf
One thing I remember the Berlin Hilton for some years ago was a stunning Sunday breakfast/brunch.