The few freelancers that work their way up and down Fields Avenue are best avoided.
There is usually a reason they aren’t working in a bar (transgender, can’t pass STD test, etc), and whatever it is probably isn’t good for the customer.
In bigger bars there may be a hundred of more women working in three groups. Customers can order drinks for themselves and enjoy the show.
When they see someone they like, they can either make eye contact and call her over or ask a waitress or mamasan to ask her to join for a drink.
It’s safest to do it during the day and be discreet about it.