a girl on one of the other forums that I am a member of came up with a you tube video on motteling. You might find it helpful.
NOTE: THIS IS NOT MY VIDEO. IT WAS DONE BY CHRISTINA, OF CHRISTINA'S CRADLE. I use a bath sponge that I got from Walmart. It is porous and soft, not hard and dry like sea sponges. I cut a chunk out of it similar to the size of my cosmetic wedges and use that to make skin tones.
Layers are a matter of taste and how many you want to do.
what I do, and I'm sure I'm leaving a step or 2 out somewhere.
1. a vinyl color correcting wash, if needed.
2. a flesh08 layer
3. veins
4. flesh08 again
5. creases, eyelid purple, blue around nose
6. a very light, light blue mottling layer with the porus sponge
7. a light blush color mottling layer with the porus sponge
8. flesh08 again or flesh07 instead
9. blush palms, soles, knees, cheeks, ears, nose, etc.
10. lips, nail beds, baby acne (if desired)
11. lips some more, blush again if needed
12. eyebrows, nail tips
--bake between all layers--
Sometimes I'll repeat the mottling steps (#6 & 7) if it is not as dark as I want it. I'd rather repeat than have it too dark to begin with.