You're just getting into the horse business, so maybe you haven't seen it yet, but you will . . . .
An astonishing number of people get horses, particularly minis, without having a clue about what they are doing. They don't know even the most basic stuff about feeding and care, never mind training or understanding the nature of the animal. It's not just horses, of course - thousands of dogs and cats get rehomed or surrendered to shelters every year because of perfectly normal behaviors that the owners couldn't cope with (but which a little bit of research would have told them were par for the course for the breed/species). Most of these people blame the animal, when the only thing it is guilty of is following its instincts and exhibiting behavior that its ancestors were bred to do.
As for training and cues, welllll . . . . haven't I told you about Blondie? A few years ago, I learned about clicker training, and had the idea that it might be fun to teach her a few tricks. The person whose tutelage I was following warned that this sort of thing becomes such a fun game for the horse, it will frequently begin to 'volunteer' the behavior in hopes of getting the reward, often to the point of becoming a real nuisance, so 1) you should be careful to choose a behavior that isn't dangerous or destructive for either the animal or anyone/anything else, and 2) it's a good idea to teach at least 2 behaviors, that the horse can't possibly do at the same time, with the idea that they can't decide which to do so they won't do either until asked (or something like that). So I decided to teach Blondie to nod her head "yes," and shake her head "no." For some silly reason, I thought she couldn't do both at the same time . . . . duh! Blondie loves to volunteer "yes," and absolutely, a horse that is nodding its head vigorously up and down is a nuisance, and it could be taken as an expression of irritation if you don't know what she's doing. Unfortunately, she certainly can do "yes" and "no" at the same time - sometimes, she keeps them separated, and sometimes, she looks like a demented bobble-head (I wonder, does that give her a headache? It does me,lol!) Incidentally, she also knows "target" and "head down," but if she's volunteering them, it's not as obvious and not a problem. But for me, this only underscored something I heard a very long time ago - while you can teach an animal all kinds of things that may work fine for you, you have to think about how these things will look to someone else. Especially for something like horses, as big as they are and as long-lived as they are, there's a good chance that they will wind up in the hands of someone else (probably several "someone's") during the course of their lives. If those people aren't familiar with you and your methods, they may not understand what that animal is doing, and they may get entirely the wrong end of the stick . . . . to the animal's detriment. That's the reason why we are supposed to teach and follow a sort of universal code of cues; to try to ensure that the horse and rider will be speaking the same language, as it were, even if they are strangers to each other. We inadvertently teach undesirable behavior all the time through ignorance or inattention, but to deliberately teach something that the horse may wind up paying for later is just plain wrong, IMO.