The brush on the left is the one I've been using to pre brush the miniatures, the one on the right is a GW fine detail brush (with about 4 hairs) for comparison. The brush I use is a cheap water colour brush that has been cut down to where the bristles are stiff and compact. They do have a slight amount of give though.
Usually, and in this case with this guys armor and skin, I mix water and paint at a ratio of about 70/30 or 1 part paint to 4 parts water. This much water means it takes at least 3 coats to see the effect but I must add that this is a safe mix (loads of water) because too much paint will ruin everything by smothering the pre brush and, if theres loads of water, it will pool in the areas you want to remain black.
So, when applying these watered down mixes, you must ensure you are not using a loaded brush.
Before I put any paint from a brush onto a miniature I always wipe it a few times on my thumb to actually see how much is coming off because its the minimal amount your after for a subtle build up of layers that don't destroy (much) of the pre brush. When you get familiar with what your mix is doing and how it works you can add more paint to use less layers or more water if unsure how a mix is going to behave.
Skin: Tallaran Flesh and Dwarf Flesh mix, about 50/50. took about 4 or 5 layers. Watered down Ogryn Flesh wash. 2 layers.
Hair: Scorched Brown and Chaos Black, about 70/30. 3 layers.
Armor: Graveyard Earth. safe mix, so lots of layers.
Metal: Devlan Mud. between 2 and 3 layers.
Armor Artifacts: Bubonic Brown. safe mix.
Blood Drops: watered down Brown Ink. this was also applied to other metal parts on the armor and hammer. 2 to 3 layers depending on how dark you want it.
Shield: Devlan Mud.
Boarder: Brown Ink.
Skeleton: Fortress Grey. small amount of Space Wolves Grey (The skulls on his armor where also painted this way).
Wings: Bubonic Brown.
Parchment: Desert Yellow. Bleached Bone.
Hammer Grip & Cloak: Scorched Brown and Red Gore mix, about 60/40. 2 layers.
Wires: Catachan Green. 3 layers. Wiped the mix off the highlight areas with my thumb.
Parchment Text: Scorched Brown and Chaos Black mix, about 50/50.
Hammer Head: Ice Blue.
Light/lens: Camo Green (even though you can just barley see it).
Theres a good bit more that could be done at this stage but he's alright for now.