I've been a few SP's first ever customer, I think, maybe a total of four or five times. I've visited an SP on her first day of work maybe twenty times, but not been the very first customer that day.
Whenever I find out it's the first day, and especially if I'm the first customer, I extend my session to longer than usual so that there's no time pressure. I tell some jokes, I try and smile a lot, be as pleasant as I can, and make everything pretty comfortable. I try to be on my best. One reason is that I can empathise a little and imagine that it's a pretty stressful situation for her; another reason is that I am pretty sure that while she may go on to forget most of the sessions she has in her career as an SP, she is probably going to remember me and her session with me FOREVER, probably in detail, since it's the very first. It'll be burned into her memory so I try and make sure it a fun experience and a good impression of me
My sense of what's going on with the SP on her very first session, from those experiences, is that she's just plain anxious and nervous about it. Not so much nervous about the sex. Nervous about the situation, about what I might think about her, how I will treat her, whether I'll think she was any good, nervous about crossing a line in society and doing something forbidden, and just plain nervous because it's something new. Usually there's also a bit of excitement too, for exactly the same reasons as she's nervous--it's exciting to transgress into the forbidden, to have sex with a stranger, etc., and it's a rush as well to get paid for it.
Mostly I DON'T think they are that nervous about the sex itself, because to be quite honest, while it's her first time having sex for money, it's far from her first time having sex with a guy. Women who opt for this as a career path either came out of some other part of the sex industry (that did not involve full service) or else have had a lot of boyfriends. So they are pretty experienced being around men and about sex, it's just the particular situation that is new and different.
So obviously that's an outsiders view. I've been there on that day and been the SP's first and watched their reaction but what was really going on inside their head? Who knows. I'd say probably a million things were going on and it was a big confusing, exciting rush for her.
I do really like being the first though. I jump at the opportunity when it comes up because it's different than a "regular" session with an SP. It's fun.