I've never written a blog before or really guided anyone through my process, but I thought I'd take a shot at it. Below is the process I use for going from initial thumbnail sketch to final digital piece.
This piece was for Threadless.com; they were hosting HEAVY METAL's cover contest, and I thought I'd give it a shot.
1. The Thumbnail: At this stage I'm just looking to get the composition right. Nothing fancy. I have a general sense before I start of where the darks/lights will be, so its really just a matter of finding the area of focus, as well as identifying the shape of the figures.
2. The Sketch: in most cases when I'm doing a fully finished illustration, I'll do the line-work by hand. In 99/100 cases, it'll be with ink (either brush or markers); but in this case I decided to do it strictly in graphite on paper.
3. Flats: Once the image is sketched and scanned in, I'll go through and do flatting. Basically, putting a flat colour under all the prominent masses in the image. This is so that the rendering process is much easier later on; if I mask my flats properly, it's really just a matter of filling in the tones like a colouring book.
4. Colour comps: I'll try as many different versions of colour until I feel the mood matches the theme. This can either be really fucking fast or really fucking slow, depending on how quickly I can find the right feeling. It's all intuitive when it comes to colour.
5. The Final Render: At this point I'm pretty much content with the image. In other blog entries, I'll go into some tips and tricks to make it look as sexy as it does when its done. For now, this is pretty much the entire process :D