Very good points were made by the others in this thread.
First of all, I need to prove myself as a customer who understands the system. I immediately ask about a table shower. That seems to indicate to them that I'm a knowledgeable customer. However a table shower doesn't fully indicate level of service available, as I've gotten a table shower not only at FS places but also some where the lady remained fully clothed and only offered a HJ.
If they leave while I disrobe, even if they indicate a towel for my use, I make sure to remain uncovered when they return, and I prefer to be erect for them to see. This again is an indicator of my state of mind and they will often grin and comment on it.
While in the table shower or the massage, when on my stomach, any attention to my butt or near the twins, I indicate pleasure either by movement or verbally.
While on my stomach on the massage table, I try to let my arms hang over the side. When the lady is on the side near my arm, I caress her calf. If no protest, I'll caress higher with each succeeding contact as she moves from side to side, going all the way to her tush. It is not unusual to find they have no undies on, in which case I'll caress that area, too. (I'm much bolder than when I first started out! Recently after having caressed the front of her panties, when the lady was standing at the end by my head, I reached up with both hands and pulled her panties off, which made her giggle.)
If they still have clothes on when they ask me to turn over, I'll ask them to take their dress off. If it is full service they usually will, and I'll get up and sit on the side of the massage table, take them into my arms and begin play.
Even if the place is FS, if you just go along with them, they'll try to make the massage last long so the playtime is short. But if you do it right you can get that started earlier. If they wanted to work on my back too long, I've rolled over, rose on an elbow and said, "Let's do something else." If they ask what I want to do, I reply "Everything." If "everything" is not on the menu, they'll advise what is.