Take these factors into consideration:
A horse is a fairly typical herd herbivore. It is mainly concerned about large, fast-moving predators. Its main means of defence is running away as fast as possible and hoping the predator gets one of the other horses in the herd instead. Its secondary defence is kicking the **** out of anything that gets in a kickable place.
Like other herd herbivores it sacrifices binocular vision for increasing the width of its visible arc - its eyes are to the side of its head. That means that it can see you coming up from behind quite a long way away, as long as you are not in a fairly narrow arc straight up the dock, but it's not very good at telling how far away you are. In the wild, predators try and approach unseen, so horses are very sensitive to movement on the edges of their peripheral vision, and particular to things that duck in and out of their sight, such as a cyclist weaving from side to side. So try to approach from as wide an angle as possible so that it can see you constantly, and ride smoothly rather than doing anything that looks like shaping to pounce. Talking calmly may help.
The rider is a secondary issue, but if you're nice to them they may appreciate it, even if it can sometimes be hard to tell. They won't appreciate suddenly finding themselves twelve feet up in the air on half a ton of animal doing pirouettes, because it's bloody terrifying, for good reason. Also, they're the ones who will initiate lawsuits.