For my Skaven I did the following;
Sprayed with grey gesso (any grey primer really)
Sprayed Calthan Brown (old
gw colour, sorry I don't happen to know its new equivalent)
Drybrush Tallarn Flesh (another older
GW name)
Paint cloth areas with whatever chosen base for cloth (mine was necron abyss)
Drybrush cloth areas with a lighter shade, in my case Shadow grey
Wood is painted scorched brown.
Metal basecoated black, and then painted tinbitz, or boltgun metal.
Teeth, claws and eyes picked out in bleached bone, Then eyes in Blood red.
Bases coated with sand, painted graveyard earth and drybrushed with bleached bone.
Then the entire unit was sprayed with a very wet coat of devlan mud. (Brushing would probaby be better looking - but this was way fast!)
A little static grass, and I'm done. Can do a unit of 40 clanrats in a night this way
Its not the bestest paintjob ever

but those clanrats can be a bit soul destroying and I'm happy with this