This is a solid case of "it is not as easy as it looks" routine. Mostly because you can appear to be in the position while not being in it at all. You will know you are in the proper horse stance when the only place you feel your fire burning is in your center and it is a warm comforting flame. For some, assuming this stance for even a few minutes can bring up some interesting internal dialogue. If you can work through this there is a state of grace on the other side.
One easy way to assume this position is: Standing straight up bend your legs slightly. This is the point that you never straighten your legs past once you begin. Align your torso triangle on top of your leg triangle by slowly pushing your pelvis towards your forward triangulation point. Your next inhale should allow your shoulders to float to the sky while you are pulling your stomach muscles up against your spine.
From as low as you can and as hard as comfortable pull your stomach muscles tight against your spine working up as you let your shoulders float up as well. Now breathe and relax your stomach muscles but don't change your position. Check your foot points and make sure you are evenly balanced. Feel your outer balanced circle and discover how much you actually can move while in this stance. It can take years to accomplish an energized horse stance. By energized horse stance I mean the stance actually gives you energy. There is no longer a struggle in fact it has become a desired position.