If you between April and November, allow for flight cancellations arising from typhoons and rain storms. This means they should among other things bring more medicine, money and other necessities than what are required for the planned period of stay.
Jay-walking is an offence. Observe traffic signals where they exist. If caught by police for violations and found guilty, fines of several hundred Hong Kong dollars are imposed.
It is useful to bring along a mask and use it in crowded places, while on the streets and using public transport.