If you get the chance, make yourself known to the CMC (Chairman of the Mess Committee) at the "pre-dinner" drinks ( and go easy on those as they lead to un-authorised absences ..more on those later !) and explain your "newness" ... he will then be more lenient on transgressions ....you hope ...
Any breaches of "mess etiquette" are usually dealt with in the form of "fines", the most common "fine" being a bottle of port. Leaving the table without permission is the most obvious crime, as is starting to eat too soon, drinking from the "wrong" glass, and anything else the CMC can dream up.. all done in the sense of "banter" and enjoyment.
At the end of the meal the Port is passed ALWAYS to the left, and the decanter must NEVER touch the table.. serious breaches of tradition to do otherwise. Do NOT drink the Port until the Loyal Toast is taken. all decanters are the "property" of "Mr Vice" .. if you like Port get close to him as he will replenish glasses as he sees fit !!
It is at this point that fines are paid .. and the fines added to the decanters....
The after dinner chat/stories/banter is as much a part of a Ladies Dining In Night as the meal itself.
Above all .. relax and enjoy ... I know you will have a great time