PAINTING:
Faces

Undercoat using a flesh colour. Then use artists oils - Naples Yellow + cadium red (depending how pink you want the flesh). After mixing the 2 on an index card (no thinner added, use straight from tube), paint over the face. Then with a completely dry and clean brush, go over the face and remove as much of the oil paint as possible. Oil paints are transclucent, so what remains gives a nice effect. Which can also be improved by more highlighting.. (but if you wish to highlight, I suggest using a darker first colour)

Faces at 15mm level, unless you are entering them for a painting competition, should be viewed at arms length. I paint my 15mm faces with a flesh tone, put a small blob of chestnut brown in the eye sockets, small lines of the same down either side of the nose, in the ear area and where the mouth is and then dry brush with white over the whole figure. This looks absolutely fine at this scale when viewed at normal table distances. IMO, it is the look of the army on the table that is important at this scale, not the detail on individual figures!

If you insist on detailing, use a size 1, needlepoint, sable brush. Provided you have chosen one with a good point, you will never need to use anything smaller.If you have an art shop near you, see if they can get hold of Whistler Needlepoint brushes. They are excellent!