Oh go on then....
Three methods:
1. White undercoat - block in colours(no highlighting), line each area in a darker shade of the main colour. Use shades wich are very slightly lighter than the colour they are intended to represent.
2. Black undercoat and paint up to the lines. Put one highlight on each area. Do the face in three triangular dabs of flesh(over red brown); CHEEKS & CHIN.
3. Dark under coat(not black). Try very dark brown or dark green or olive drab or dark grey(dependant on the colours going over the top). Use same method as 2 above( this gives a gentler look and not so stark as black undercoat)
Use undercoat as in 2. or 3 above and dry brush your main colour highlight then tidy up with a black or dark infill and paint the detail.
SEE there's four methods not three!!
I used to do 3 & 4 but now use 2. NO BLACK UNDERCOAT - Olive drab.
Cheers
B