Hello Jack !
It's a difficult work so you definitely need to love it, to love being around horses almost every day, for a great amount of hours. You have to be good at explaining things, to be understanding.
And of course, you have to know horses and how to take care of them and ride them ;)
I think the most important thing is to be passionate, when you love what you do you, you are obviously better at it ! You have to have experience, patience, the desire to pass on,...