How to bargain in Hong Kong?

Excuse me, could you please elaborate on the process of bargaining in Hong Kong? I've heard that it's quite common in the local markets and shops, but I'm not sure how to approach it without seeming rude or offensive. Are there any specific etiquette rules or phrases I should be aware of? Additionally, how much should I expect to negotiate down from the initial asking price? Any tips or advice would be greatly appreciated.