Heres What You Should Do Scaz...

Theoretically- Fluff a couple of pillows up, get comfy, hands behind your head, and lay back, enjoy the slurping. I mean show. The pillows are important too, so that you still have a good view when our head goes lower for giving the boys some attention. Its all in the details you know.  

It's case by case.

We're all different.  Some want you actively involved.  Some want you to voyeur.  
At a first meeting, I try to mention that information just before I begin dictation.  I want you to know what I'm comfortable with as we begin our mutual exploration.  If she hasn't mentioned it in the first few minutes of enjoying you, I think it would be appropriate to ask.  It's your meeting after all.

well typically when friends are with me one hand is usually already occupied " its in a tight fist as they're biting down on it" trying to hold back.... hehe smiles!
You can do what you want with the other but that's usually in a fist pointing towards the heavens.

Just saying
Barbie out