This is how I do:
1) black undercoat
2)* Basic colours
3) Overbrush Vallejo Green-grey sloppily all over
4) Drybrush P3 khaki
5) Wash with Vallejo matt sepia wash
6)* Paint on very thinned nuances like washes (for clothes, hair). Skin gets a mix of sepia wash and humbrol green.
7) Sprinkle-splatter it all with a toothbrush using a mix of tamiya red, humbrol blacks and browns.
The good thing about the method is that it's very well suited for conveyor belt like painting so that 200+ zombie horde is suddenly within reach even for people who go somewhere everyday from 8 til 16..
*These steps can be excluded but it'll of course lower the quality of your results