Use eyedropping tool between values to get smooth shading instead of smudging things together or using large smooth brushes.
What about healing brush to help smooth the shading? Of course that kind of blurs the image which isn't good (and I don't know how the brush reacts in Photoshop, only GIMP).
And I've never used the "Spot Healing Brush Tool", just tried it out for a few strokes. Don't like it, much too little control imo. That's just for a first time test of it, though. But it seems messy.
Anyway.
Cen did me the favour of pointing out some flaws so I adjusted a few things, and then I lost the will to continue. Added a few quick highlights to indicate his metallicness, but yeah. Probably won't finish it.
Reference used was a pic of a Welsh Mountain pony I found through a quick Google image search, and a greyscale colouring sort-of-not-really tutorial I found on deviantART.
Really wish I could draw horses (or as it is, ponies) properly... If any of you can spot some consistent, glaring anatomy/proportion errors in these, please point them out to me. Aside from the legs. They're supposed to be long and stiltlike due to character design. Possibly bad design, but I like him that way.