Diffuse Colour: Leave that for now we can change it later.
Diffuse Strength drop to 90 – 80%
Specular: In reality spec colour is always white; it is the surfaces properties that can give the spec colour so I generally use White. Well that is how I understand things. Some vendors use a light blue colour. It is up to you what colour to use.
Glossiness: About 30 – 40% should make a nice start
Spec Strength: 8 – 10%
Spec 2. I still don’t know what or why there is a Spec 2. But this is one of those setting that can only be set up right when you turn off Spec 1 and test the spec 2 only. When you have the desired effects then reengage Spec 1 and test.
Anisotropic: Not for skin. Metals and Glass etc.
Ambient: I never use Ambient on Skin…ever.
Reflection: Some folks use a Reflection with an Environment Map (HDRI) but I have never had much success with this. Given you skin is generally oily having reflection does make realistic sense. If you want to have real (raytraced) reflections at a very low setting expect a longer render.
Fresnel: Not on Skin but good for Eyes mainly the pupil.
Velvet: Colour well this is a personal choice but after some testing I found a colour similar to the skin colour best like a peach/brown, 20% strength and about 15% falloff
Colour I always start with a 128, 0, 0 red and adjust up or down if needed. Want more red SSS increase the red and vice versa. However if there is too much red burnt in the skin texture maps then injecting red here will make the skin appear more red. To counteract this drop the red channel in the diffuse colour.
Strength depends on a few things, like are you using SSS maps then 100% should do it. No SSS maps then 20 – 50 % might do it.
Refraction: This is a good one as most scientists can’t agree what the IOR of skin is as there are so many variables but a value of 1.39 – 1.41 should do.
Scale: is how thick the surface is before the SSS takes place. This is something else I need to test and we don’t really know what value this is. If it is the Daz Studio default then 1 = 1CM and our skin is so much thinner than that. I have been trying to find out. IMHO 4 is why too high if this is the case. But with anything like this I say just go with what works. LOL I generally use a value of 1 to 1.70 before someone got me thinking what the value is.
Group: Is for grouping any surface that has the same SSS properties this is so the render engine knows what SSS properties applies to which surfaces. I use SSS on Teeth and Eye whites which have different SSS settings so I make all the Skin group 0, Teeth group 1, Whites group 2 and so on. If you don’t do this the render engine will lump all SSS together and render the whites and teeth with the same SSS settings as the Skin.
Translucency: I never use for skin. The SSS should give use what we need.