See map of public transport in the Hague, HTM: From Hollands Spoor, take tram 11 direction Scheveningen Haven, tram stop “Willem de Zwijgerlaan”. Just a little further down the street you can also use the tram stop of tram line 16 (as of May 2, 2016). Just take the tram to the end (“Statenkwartier”) but leave only after the end loop at tram stop “Frankenslag”.
Parking on the street and in the surrounding area is free between 00:00 and 13:00 hrs, between 13:00 and 24:00 hrs parking is subject to a charge. More information about parking near the Statenkliniek can be found here.