Reminds me of my attempts at painting rather than sketching! I recommend first off that you use reference if you are not already.
I suggest you simplify, the shapes and likeness is there! But it feels muddied at times, I think because you are trying too many shapes and colors at the same time. Try a 2-tone or 3-tone piece. For 3 tone, that would be base, light, and shadow. Look at comics & manga for inspiration. They get away with a lot by doing very little.
By simplifying into fewer colors, you force yourself to "edit" the picture more; to digest it and then re-render it your own way. Always look out for shapes that can be unified together into a larger one.
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