there is no magic formula for painting faces
it is very simple - how much effort you put in painting them, such results you will get
for modest results you need 3 painting phases - basic flesh tone, I'm using for this Model Master enamel 'warm tint' over light grey priming, than some basic shadows on the face with some darker colour, and finally highlights with a lighter flesh tone - some beige is the best fot that
it is not difficult at all, but needs time, there is no speedy way to do it
another important thing is to thin the colours, and use the best paintbrush you can get
when considering paintbrushes, it is not about how many zeroes they have, but how much you paid for it
expensive 000 paintbrush is a 100 times better than cheap 00000 model, which are worthless
start looking for the 10 euros+ paintbrush
one is enough
and use only the smallest amount of thinned paint on the first 2 mm's on the tip of the brush
it will
not dry on the quality paintbrush
if you want to speed up the painting process, you need to paint in batches
you can't skip the steps, but you can paint 3-4 figures at the time
very helpful thing is to look what others did, and what colours they used
so when you find the authors which work you like, observe the colours they used instead of admiring the end result
which colours you can see painted, it is what they used to paint the faces
simple, but nobody is actually trying to 'decipher' the colours used
it is not important who makes the colours, but to find an adequate tones
my favourite authors are Erik 'entrauner' and Ben and Jen 'Victorious Secret'
hope this helps