If you have never been to HK,buy a HOHO bus ticket. Lets you get to see a decent amount of the city and you get priority to skip the often long lines to get a ticket for the Peak Tram ride up to the top of Victoria Peak.
Hope you can find a place to shower when you get back to the airport as the heat index was really bad when I was there a week ago. I cannot imagine getting back on a long haul flight dripping in sweat!