This is my reference photo.
Start by drawing lightly the basic shapes of the horse. Remember that this is the basic shape of the horse. It doesn't have to be perfect.
Now draw the outline of the horse by being more exact with your lines. Use your basic shapes as an guideline and don't forget to refer to your reference photo.
Erase any unnecessary lines. This is why I said to draw lightly.
Now add some detail to the face and add the ears, tail, and mane.
Now add some shading to the legs.
Next add some shading to the head, neck, and shoulder areas.
Shade in the mane and tail.
Lastly, draw in the grass.