Lovely work!!! Keep up the practice and you'll be fantastic!!! Try to draw as many different horses as you possibly can, with all different angles. It'll help to improve your 'eye' for drawing and improve your work ;)
You've got a good knack for getting tonal values as well, only thing I'd suggest is to darker the top of the inside of the horse's nostril, to balance the tones across the whole drawing as it's a touch 'top heavy' (all the darkest bits are at the top of the drawing).