There's really good advice on HK on the punting wiki.
I am aching to go, love the idea of just walking around a skyscraper full of chinese whores 
There are some lovely looking Russians and other 'exotics' on that site as well 
Yes it's quite the experience. If you can get over the overall seedy-ness of the environment you can have a good time.
Find a door that's available. Knock. See if you like the girl, then agree or not.
Go in and do the business, or, simply say no thank you and try the next door along haha
I'm more for the Caucasian variety so usually sniff out the Russian/EE girls in the various buildings. None the less- it's quite exciting!