Description
Just practice.
I found that the most important feature on his face is probably the fact that most of his mouth is hidden. Also, his jaw hinge is probably quite far back, but his mouth is quite small.
Closeup of the skull: fav.me/daxvu3m
I combined features from the skull of a hawk, a cat, a hyena, and for the nose, a horse. I found the hawk skull fit surprisingly well, since Trico doesn't have any teeth. Trico, in form, is sort of like a bird that evolved to fill the ecological niche of mammals, and over time the beak got internalized. His neck is also very bird-like.
Visually I think Trico resembles a hyena quite a bit, with the tear marks of a cheetah and the feet of a cassowary.
Feel free to reference.