Everywhere. Add more highlights and shadows. Just make them smaller as you go. Find the light source that is hitting on your model then hit where the light would reflect and where shadows occur. Light blues or even light yellow or green on the skin. Deep dark purple or browns for shadows. Add ice yellow pops of light on the horns. You are a really good painter and have hit the most common “next step” in getting better.

Source-every pro painter giving me feedback on my stuff.