Know what you want. Short strands? Earrings? Custom length ropes or skinny bracelets for gifts? Any way you like them, the Kowloon Jade Market has them. Booth after booth carry pearls of all shapes, colors and quality. Take a lap around and decide what you're really after.
Decide the market. Most long ropes go roughly for around $10.00 USD, but if you're buying several you can likely get an even better deal than that. The asking price will be far more, so put your game face on and deal.
Know you're getting the real deal. See the article on how to detect real pearls from fakes to conduct your own onsite tests while shopping. Color, weight, texture and regularity are all factors in examining true pearl quality. For inexpensive costume pearls, you may not care. If you thinks you're buying an $800 Akoya pendant, it might.
While there are fakes out there, the real ones with the right prices are not hard to find... look for the booths with the crowds of shoppers.