By sort of request:
This is the original scan, it was done in one of those moleskines with the thin paper (I can't bring myself to buy the ones with the thick paper - not enough pages) hence all the visible writing. The contrast has been pumped up, and on an overlay layer I scribbled in some colours. It's always red, muddy yellow and green. Always. It's like the bottom half of the spectrum doesn't exist.
On a multiply layer I've blocked in some brown, trying to work out what the hell I was trying to describe with those pencils.
New layer, no special properties. I just picked out a few highlights, trying to visualise some form and detail. I made a bit of an attempt at surface texture.
I always knew the background would have to go, so on a new layer (just in case I went over something I'd want to restore later) I blocked in some white. There's some more rendering, some decisions being made on what the hell those ears are doing and general noodling. This stage took a lot longer than I wanted so I set it aside for a few months.
This is an image at 100% pixel size. I'm in the habit of making work for print (just in case!) so there's a lot of room for detail. My general method is to just move around the image, filling it out. Most of the colours are there already so my finger is just hovering over alt to colour pick with each stroke. The aim is to make sense of all the chaos introduced by the previous steps - edges are blurred or sharpened, rough textures are smoothed out and shapes are refined. After a few hours of nit-picking and noodling, it's done. More process posts can be found here (they all say pretty much the same thing...).