I think you did a really nice job, Paints. (:
I concur with PintoTess, too. The bridle is a foreign object on the horse's face and there should be a lip (a "bump") where it wraps around the animal's face. I also agree about the ears. A good way to fix this is to look at the drawing in the mirror (seeing it backwards, upside down, etc. can help you see some mistakes yourself). If you're using a reference (which by the way, can we see that as well?), keep referring back to it. Compare your drawing to the photo(s) and say; "what looks that same, what's different?" The horse's head, too, should be a little bit more narrow; especially at the muzzle. As you can see in this
photograph I took of one of the livery horses, the face narrows out quite a bit. Something else I noticed is how "flat" the mane is; it's laying against the horse's head, which unfortunately makes it look almost bald (oh noes!). Add a little more "hump" in the forelock and some simple shading and you're on your way to improving manes!
Since no one is a perfect artist, there will
be anatomy quirks. Work around those, they're no big deal. You're young and have plenty of time to improve. (:
You're on a great track; studying photos is a great way to start, especially when you're detailing the drawing and not just doodling something simple. Way to go!