Ghetto speedpainting tutorial!
I can't remember if I started on a huge canvas or if I started on a small one, blew it up, and then painted on it some more. Whatever, either way works. The final image was 3000 pixels high.
Step 1: Set up a dirty ground- start with a midrange base color and slap a bunch of other colors and textures on it.

Step 2: work out the composition with big big brushes. I know this looks like trash, but it's better to put down something and then compeltely obliterate it then being careful, being neat and erasing stuff; at least for me it is. This is the part where you've got start to think about what you want to say and how you can say that in the most direct and simple possible way. The simpler you can reduce your idea down to, the stronger your final design will be. Plus since it looks like crap anyway, you can afford to take risks and just put down anything and see if it works before deciding to move on.

Step 3: Worked out the basic gesture, perspective and space. Also you can see the whole blood dripping idea coming into play- I wasn't sure it that's work or not, but I wen twith it anyway.

Step 4: I know this seems like a huge jump and it is, but really it's just continuing to define the stuff already established in the shitty stages- all this part is is rendering. I used some textured brushes and some red brushes with scattering on them to get the 'rough' effect.

Step 5: threw in a some red/orange textured brushwork on a color dodge layer for extra glowwiness.

Step 6: Again, this is just some more rendering going on, focusing on the upper torso area and the shiny stuff.

Here's a detail of the actual resolution this is painted on- notice that you don't really need to render every single detail- in fact doing so will usually just suck the life out of a painting. Try keeping your deatils to a minimum amount of detail, using discreet use of single brush strokes to get the basic idea across- nobody cares about a single link of chain, but they do (or I do, rather) care about getting the message of there being masses of chains there- get that across without getting stuck on one idea or area.