I have come to believe that as long as your piece is secure in a stand and you stop touching it once the shapes are in, you can smooth with tools over the surface, use brushes and finally some solvent. I use a gentle one like Vasilene.
This forgoes the need to sand I have found if done right.
Also, I have discovered that plastic Cake Décor tools do not melt or pit from the plasticiser and flow more smoothly over the surface. Perhaps this will be of help to you all.
I know when I started with sculpey, I used to hold my sculpt despite a Pro telling me not to touch the clay except to apply it. I also wear Nitrile gloves which I find helps reduce or eliminate dirt. So the main thing is ....
Secure it
don't hold it
don't smooth by hand if not wearing gloves- better to use a tool, it's clean
clean yer hands with baby wipes
and wear gloves. This has helped immensely.
hope this is of interest to you all.
atb --tim