I think that you should focus more on the actual form; the lights and shades and edges. Do you normally draw out lineart in black first? Or block in colours?
I personally like to block in shades with a larger brush, and then refine paying closer attention to the pixel level. Here's an edit, I've first blocked it in in tones of grey, I don't always do that but it can help you to pay close attention to form. After that, there's refinement, tweak outlines, add a highlight and shadow colour or two. After that, recolour the greys. I did a couple of quick ramps which employ hue shifting. Hue=the actual colour, e.g. red, yellow, whatever. In nature things' shadows generally are closer to the purple to blue shades (Not necessarily actually purple, but more purple). Highlights conversely go closer to yellow. Those aren't hard and fast rules, but they can help if you're a bit stuck
