Cassa Belle said:
the white markings look great! Just make sure to add a bit of pink where needed, for example a tiny bit on the nose.

The horse is a bit too smudged out and so is the tail. The mane looks quite good though!

Try adding some highlights and lowlights to the horses body ;)

also keep in mind lighting, the lighting is coming from behind the horse, so keep that in mind when making the piece.

Amera Eventing said:
Fantastic job!

First thing I noticed is the stiffness of the hair. The mane and tail have a natural flow the them and will wave around, not stick straight out. Try to incorporate that movement.

The light source is also behind the horse, from the sun, so try and add some light hitting the horse from the back.

The spot where the legs flow into the grass seems a bit rough. Try making it a bit more natural by having a sharper cut with several strands of grass visibly covering the leg, not just a blob of leg and a blob of grass.

Since the horse is the focus of the avatar, try to blur out the backdrop a bit. The sharp clouds take a lot away from the subject.

Keep in mind the horse would also be casting a shadow on the ground from the sun.

I think you're on the right track though! Great work! :)