Chinese and English are official languages in Hong Kong. Government publications, public transport and utilities signage, street names are bilingual.
The major spoken language of street level is Cantonese. English is still the popular language of international business and most people who come into contact with foreign tourists speak at least a smidgen. However, the use of Mandarin (Putonghau) has been on the increase since the Handover in July 1997.
It is good to have your destination written down in Chinese, and to carry a printed card with the name of your hotel in Chinese.