With only one day in Hong Kong it is best to take a half day early morning city tour which will cover all major spots of interest including the Man Mo Temple, the Victoria Peak, Stanley and Aberdeen. If with family and children, maybe Ocean Park can be chosen instead.
Stop for lunch at suggested restaurants depending on your budget. If shopping is your criteria, then a trip down Causeway Bay or Nathan Market is a great idea for a couple of hours. The upmarket, Pacific square or hipper malls may also be chosen.
In the evening, a sunset or night cruise around Victoria Harbor on Star Ferry with the Symphony of Lights show is an absolute must. For dinner any of the restaurants with a view of harbor lights, should be chosen.
If one still has the energy then going to the Temple Street Night Market is a great idea, especially to sink in the atmosphere of this buzzing place. If looking for some more action, a trip to the bars and nightclubs of Soho can be taken.
By the end of this day a great sleep is guaranteed the moment one hits the bed!