At the risk of sounding snarky, I am going to comment on how I do not appreciate people who come in here and say how much their artwork sucks. I don't think you would want to post your drawing if you really despised it as much as you advertise. I don't mean to pick on you only because I have seen many people come in here and talk about their "crappy" artwork. It almost seems like in saying your art sucks, you just want to fish for compliments. I know I occasionally put out a drawing that I am not entirely happy with and I may express that, but I would never just come in here proclaiming my art to "suck" and then leave it at that. I don't know, just kind of strikes a nerve with me because I think all art is beautiful if it comes from the heart.
I can understand if you want to come in here looking for advice in which case there are many people here who are very helpful. I have personally taken my art to the next level after some of the advice I have received here.
Anyway, I am not sure if you are coming here just to show us your drawing or if you would like some advice, but I know a lot of people have benefited from taking a certain area that they find troublesome and then just focus on drawing that part rather than the horse as a whole. In your case, it would be the muzzle. Try to find close up shots of just a horse's muzzle and practice drawing it. Then after you have gotten in a little practice, apply it to a full head shot, I hope this helped. I think you are off to a good start and you have the basics down pretty well. It's all a matter of practice.
Please don't think that I am attcking "you" because I am not. I have just seen a trend of people just starting out who belittle their efforts and I just don't see that as being productive, espciecially if you want to continue to refine your skills. It's counterproductive in my opinion.