Have not done a threesome myself, but the consensus seems to be that, yes, if you are just going to show up to the bar and go from there it is best to pick a lady and let her suggest a girl she is compatable with. Conversely, you could direct message girls you were interested in on twitter and perhaps make a connection that way, arrange a threesome prior to arrival and call the Ranch to make a reservation with the ladies involved.
Hanging out at the bar is a good idea, and you can look through the website and see who will be here the same week as you so you can start thinking about who you might like to meet. You can also email the ladies you’re interested in having a threesome with and ask if they are interested in partying together. 🙂
You can negotiate with one lady first if you’d like, or you can pick two girls in the bar and negotiate with them at the same time. It’s entirely up to you!