I like what is written so far. I like to say to people, "Draw what you SEE , not what you think you see". But, she has explained it better.
I also like to think about the lines of energy in a painting. For horses, these will flow down the neck and spine and one must think about how this very heavy animal is carrying its' weight. So, I kind of think of that line of energy to the ground (if the animal is standing).
Or, maybe I should say, I think about the bones of the animal under the skin. I need to be able to feel the bones and where the should be in ordre to make the drawing look like it really bears weight. In order to do this, I often literally try to stand myself in a position that mimics my subject so I can feel which leg is more weighted, which hip stick up, which shoulder is above the other, things like that. I can "feel" an empathy with the position of the subject if I literally take up that postiion (in pretend) myself.