Here are a couple of different methods on painting Skaven.
I usually paint 5 models at a time, and I do each step to every model before moving on to the next stage.
Undercoat: I spray undercoat on the model and shield sprues. I usually use White to make the colors brighter.
Fur:When painting the fur, I use Bestial Brown, shaded with Brown Wash, and drybrushed with Vermin Brown.
Flesh: I paint the Skaven's flesh with Bronzed Flesh washed with a watered down Chestnut Wash. The teeth and claws can be painted Bleached Bone.
Clothing: I use drab colors for the clothing. Any dark color works well, dark greens, blues, reds, and grays are my favorites. I try to avoid browns as it makes the model look boring. I paint the belts and othe miscellaneous straps with Snakebite Leather.
Trappings of War: I paint the armor, weapons, and shields and bosses black. Then I paint Boltgun Metal over them (only the bosses and rims on the shields).
Basing: I paint my bases Dark Angels Green, then coat it with PVA and flock it with white sand. Then I drybrush Goblin Green over the sand. I follow that up with a drybrush of Snakebite Leather over the sand as well.
Finishing Touches: Glue the shield on. Give the model a coat of Gloss Enamel. After that is dry, I spray a coat of Matte Enamel over it. The gloss protects better than the matte finish, but I prefer the flat finish for my Skaven. This way I get the best of both worlds.
Since Skaven regiments are so large, the most practical way to paint them is in large groups of at least 10. Paint each stage on every model before moving on to the next bit. This allows the paint to dry on each model.
Stage 1: After assembling the models, give it and the shield sprue an undercoat of Black paint (leaving the shield on the sprue gives you something to hold onto).
Stage 2: The skin and fur is the first thing to paint. Drybrush these areas with Scorched Brown and then go over the fur again with Vermin Brown. Drybrush the shields with Bestial Brown.
Stage 3: Paint the skin area with Dwarf Flesh. For the clothing try using Dark Angels Green and Bubonic Brown. The straps and belts are picked out with Bestial Brown. Drybrush the shield bosses and rims with Boltgun Metal.
Stage 4: Paint the armor and weapons with Boltgun Metal. The teeth and claws can be picked out with Bleached Bone. The base is painted Goblin Green and flock is glued on with PVA. Finally, glue the shield into place.