Basecoat the skin with a mix of 3 parts Cadian Fleshtone , 2 parts White and 1 part Administratum Grey . This is quite a complex mix, but you only need to do it the once. I would advise mixing a decent amount, then just taking a small blob whenever you need it in future steps.
Add a small amount of Black Red to your skin mix, in a ration of roughly 1:2. Then thin this mix with a substantial amount of Lahmian Medium , until it is at a glaze consistency. Now use this to glaze in some general shading, going extra heavy in areas that would be sore, like mutations and boils.
Add some Khorne Red to the above mix, then enhance the shading around the mutations and boils. You could even go for some pure Khorne Red in areas you want to look extra bloody.
Now mix some Black Red into the original base colour, so it is roughly 2:1. It should now be noticeably darker than the initial shading step. With this colour, add more selective shading to all the areas we didn't classify as "sore" in step 2.
In particularly dark recesses and folds, add definition with a small amount of pure Black Red .
Now mix some of the original base colour 2:1 with White and add some very general highlights.
Increase the amount of White in the mix, so it is at least 1:1 with the base colour. How highlight more selectively.
Finish with a few very small and selective highlights of pure White . Add only to places that would really catch the light and the centre of the spots.
Eyes
Pick out the eyeballs with Wild Rider Red .
Pain the majority of the eye with a 1:1 mix of Wild Rider Red and Flash Gitz Yellow .
Paint the centre of the eye with Flash Gitz Yellow .
Finish with a specular highlight of Ice Yellow .
Black Claws
Basecoat Black /
Glaze highlights in with Stegadon Scale Green .
Mix some Stegadon Scale Green and Sons of Horus Green for edge highlights.
Now add some Screaming Skull to the above mix and selectively highlight.
Finish with Screaming Skull on points, where needed.
Open Mouths
Basecoat with Khorne Red .
Wash with Barak-Nar Burgundy .
Paint the deepest parts with a mix of Abaddon Black and Khorne Red . Keep this thin, so it floods the recess.
Highlight internal details with a 1:1 mix of Khorne Red and Screaming Skull .
Brighten the mix with even more Screaming Skull , and add final selective highlights.
Teeth
Basecoat with Steel Legion Drab ..
Chunky highlights of Karak Stone .
Smaller highlights with 1:1 Karak Stone and Screaming Skull .
Selective highlights of Screaming Skull
Finish with small White highlights.
Tongues
Basecoat with Khorne Red .
Shade with 1:1 Khorne Red and Abaddon Black .
Glaze the open and exposed areas with Mephiston Red .
Add chunky highlights of Evil Sunz Scarlet .
Add fine highlights with 1:1 Evil Sunz Scarlet and Deepkin Flesh .
Selectively highlight with Deepkin Flesh .
Add specular highlights with White .
Hair
Basecoat with Eshin Grey .
Drybrush heavily with Dawnstone .
Repeat, but lighter with Administratum Grey .
At this point, decide which portions of the hair you want to be light and dark. Glaze the dark portions with Stegadon Scale Green and the light with a mix of Administratum Grey and White .
Finish by highlighting the hair with the colours you already have out. You can probably get away with a few edge highlights of White on the light portion and various combinations of Dawnstone , Administratum Grey and small highlights of White on the dark.
Dirty Cloth
Basecoat with Grey Seer .
Glaze in some very general shading with Fenrisian Grey , defining the shapes and folds.
Mix the Fenrisian Grey 2:1 with Rhinox Hide , then refine the shading.
Increase the amount of Rhinox Hide in the mix, and add even more precise shading where needed.
Now we will dirty up the cloth, focussing the majority of in towards the bottom on his top. We do this using 1:1 Grey Seer and Dryad Bark . This paint is applied with a mix of stippling, scratch lines and glazes, applied as seperate layers.
Repeat with pure Dryad Bark , coverring a smaller area and focusing even lower.
Now highlight the cloth with 1:1 Grey Seer and White . Apply this as quite chunky highlights on the "clean" bits of cloth and as a pretty uniform fine edge highlight on the "dirty" bits.
Using White apply fine highlights to the "clean" cloth and very small/specular highlights on the "dirty" bits.
Wood Handle
Basecoat with Dryad Bark .
Wash with a a dark brown. I had some Abaddon Black and :rhinox hide on my palette. So I just thinned it and used this.
Mix some Karak Stone into the Dryad Bark and highlight.
Highlight more selectively with Karak Stone .
Finish with specular highlights of Screaming Skull .