I can see you're off to a great start! Your outlining is very good for a beginner, you have an understanding that its just not circles and straight lines. There are grooves and dips and things that stick out. I don't know how much of a critique you are wanting, if you want more or less let me know.
I agree with Flintlock, draw a lot lighter with your outlines. I can barely to get lines I draw to be picked up by a scanner and I still draw too dark. I would also encourage you to venture into some shading. Look for shapes in the horses face, see where the light hits (or doesn't hit) see where it creates shadows.
Then from there the horse starts to stand out from the paper. There is shading that goes on under the cheek bone on both the neck and face. The face also has a lot of lines and wrinkles. There are a lot around the eye, and some major ones in the nose. Don't be afraid to look for and add those details!