Fantastic job on this. Your lines are clean, great shading. I also love the amount of detail you put into the background.
My one gripe with this piece however is how you shaded the mane. It doesn't look very natural, it seems you just shaded it in like one would do with anime hair. Also, the lines you drew on the tail don't look natural. They shouldn't really be drawn in that severely, but rather blended in with the mane.
I can also tell you erased to create the highlights. When I first started drawing hair, I used to do this, but I hated how the eraser would smudge, which seemed to happen here.
To make the mane more realistic, you could try to separate the mane into different parts and using pencil strokes to follow the flow of the mane (I'm sorry I'm terrible at explaining). Also, use the whiteness of the paper itself to create the highlights.
I hoped this helped.