If you watch horses in the herd, I mean "really" watch them, you'll see how good they are at watching body language.
And not just body language, but subtleties you and I would easily miss.
Nearly every time I feed two of my horses, the alpha horse always pins his ears as the other approaches.
The other horse instantly sees it and backs away.
Pinning the ears is all it took.
And if you didn't see the ears pinned, you wouldn't have known what was going on.
If you want to be good at controlling your equine then you must practice controlling your body language.
Now when you want your horse to move forward, back, or sideways from you then use your body language to help you.
Stand erect.
Your movements toward your horse must be purposeful and exhibit leadership and confidence and confident assertiveness.
On the other hand, when you want your equine to stay with you, or stop in the round pen, or slow down then your body language should soften.
Don't necessarily stare him in the eye.
Another cue I always do with equines is leaning slightly to one side and looking at their hind end.
When I do this, they move their hind end away from me at all times.
But I had to teach them this body language.
They didn't just move because I leaned at looked at his hind end.
I first had him in a halter and lead rope and taught him to yield his hindquarters.
Then I transferred the cue to when I lean slightly and look at his hind end, he moves it accordingly.
Heck, you can even transfer the cue to point at his hind end and he'll move it.