Here's an already-posted (in a different thread) link to a video showing the facial reactions and upper-body movements of spanking actress Lily as she's being spanked bare-bottom with a hairbrush by her supposed 'big sister,' Kailee:
http://spankinggif.tumblr.com/post/57081242851/view-of-lilys-face-as-kailee-spanks-he rKailee's remark that "I don't think you'd be crying if you didn't do something," that struck me as a rather dubious assertion. Couldn't Lily be sobbing loudly over being paddled so soundly even though she was innocent of any immediate wrongdoing (at least that she was aware of)?
Here's the *counterpoint* (also already posted) video link, showing Kailee's facial expression (plus Lily's sweetly-reddening bumcheeks and plenty of effective steady smacking with the VCS bath brush) as she spanks her 'little sister'--since she's purportedly walloping the young lady's derriere merely at their mother's direction, Kailee's facial features predictably show simply an "efficiently doing my job" look:
http://spankinggif.tumblr.com/post/57081287557/view-of-lilys-butt-as-kailee-spanks-he rMy ideal preference in the reading (and writing) of spanking-oriented literature is a shared focus on the emotions of both spanker and spankee; since in my case the female disciplinarian is the character I tend to be attracted to, I'm interested in her feelings (and the facial expression reflecting them) as well as those of her punishment recipient, whom I generally identify with personally.
That requires one of the following points of view--third person (omniscient), first person by a witness to the spanking (although he/she would only be deducing the exact emotions of the direct participants via observing their reactions) or shifting first person to narrate the feelings of both spanker and spankee, plus possibly even the 'visuals' of a watcher who could view both participants' faces.
The physical responses of the person being spanked--squirming, squealing, kicking, crying, howling, perhaps finally just moaning in surrender with little movement--are important to me also, thus I do prefer a fairly detailed description of the chastising process itself.
As for physical descriptions of the characters (sometimes including their clothing), as a reader I don't generally find them necessary (although I do appreciate them), but as a writer such a personal description does often help 'ground' me to that individual, making it easier to relate to him/her. (Yes, I also have an unrealistic tendency to make those fictional persons, whether youthful or middle-aged, considerably above average in terms of overall attractiveness.)
However, I do usually attempt to include character descriptions within the natural flow of a story, which is how I prefer to read them as well...

--C.K.