It's really good. Im no expert or anything, nowhere close to one, but i can maybe tell you a tip or two?
First, the eye looks like it MAY need to be a little higher... it's not too bad though...
Next, you see the top line of the halter/bridle? Well it's kinda running into it's neck. I think it needs to be angled so that it doesn't look like it's digging into it's neck. Also, the top of the halter, depending on what kind of halter you're going for, seems to need a little editing... It seems to run into it's horn...
i found these for examples, if they help...
this and
this.
They have two different types of halters/bridles on. The second is closer to the one you drew here tho
Like i said, im no expert of anything, i just hope to help you out some