What are the "rules" and recommendations for a new client to follow on the first encounter and when communicating prior to and at the first meeting?

Rules do not exist. But application of common sense is advised. You have found your way to this site. Get a VIP membership and use the review search engine to make your choice of a provider.
When contacting a provider for the first time give only information on the day and time that you want to meet. There is no reason to go into any detail concerning what services you want, you should have figured that out through your reserach on the provider. Either decide that you can supply the verification information that the provider ask for or that you cannot, careful providers will not tolerate attempts by you to determine what information she gets from you. If you are concerned about giving the information that she request move on to a provider that request information that you are willing to supply.
It is a good ideas to have good body and oral hygiene at all times, but is particularly important when you expect to get close to someone and have them get close to you..
Once in the presence of the provider behave like a calm gentleman and allow her to make the first moves. If you have made the right choice, she will pull all the right strings early on and throughout the session.

Feel free to go ahead and tell the girl that it's your first time using a service.  Actually use the words "using a service," as opposed to "seeing an escort;" it sounds more dignified.  Most providers will be very understanding, and accomodate you accordingly.  Some may talk to you a little help you relax, some may start things off with a massage, and others may even give you a brief overview about their profession in general.  If she's a reputable provider, she sincerely wants you to relax and have a good time with her.