The shading. xD I can see a bit of attempt around the edges, but there needs to be a bit more. Also, judging by the color of the 'shadows' you tried to horribly abuse the Burn tool. Try switching it to Dodge, set the strength to something low, like 3% or 5%, and use that for highlights. Try to look up pictures of dogs to get a better idea on where more light should show based on fur length and muscle.
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