The contrast & darks on nose & horns grabs my eye the most right now, are they really that dark in your ref? Strong contrast in an area will tend to become a focal by drawing the eye there, so be aware of that if it's not really where you want a focal/eye grabber..
also any hard lines grab the eye.(nose/horn line)
Maybe softly add some blue to the blackish shadows on his leg?
Same for under body, a blued or purple toned shadow is more appealing than gray or blackish shadows..
* Camera & photos rarely show darks /shadows as the color we might see in real life.*
You can use artistic vision to make shadows more interesting than black/grays that can look sooty..
You could add a far hill in a soft blue tone in the empty slanted are on the lower right.
This is an image I came across..similar pose-
far side of body (horn/ rear legs) should be slightly smaller than the nearer side to viewer..perspective thing..