hi there!
so far you've been making an awesome start to art
Here's a few tips that should help as well as some questions
1. Hooves
with landscapes such as snow, sand, etc the hooves need to be 'blended into the ground'
this includes thing such as blurring some of the hooves, recreating them and rubbing parts out
2. Shadows
these are something a lot of artists forget, including myself. Sometimes all you need to do is duplicate the horse, turn t pure black and flip it upside down to match with the horse. Or even just squiggling some black marks under the horse on a new layer
3. Natural colour
another thing some newer artists struggle with is making the horse look natural in it's landscape. To do this you can do something as little as playing around with the following tools
curves
colour balance
Brightness and contrast
4. Manes and tails
some artsts will draw these from scratch wihile oters smudge, I tend to use the smudge tool to do mine as it makes them more natural, depending on your program you can PM me for help [gimp 2.8, ibis paint x]
and a few question
1.
how long have you been doing art
2.
what programme do you use
3.
how do you do art [tablet, finger, mouse, etc]