There are 2 things you could make a dragon rider:

The first would be bending a dragon's will. Often through a magical item or magic in it self. Like a horn to command a dragon. Though if you do that, it marks the bulk of the dragon's unintelligent and controlable. In other words, a little less awesome and powerful on the mental level. If you ever read A Song Of Ice And Fire (or saw Game of Thrones) then the Valarians used a magic horn to control their dragons.

The second, more used way is like Toothless from How To Train Your Dragon or Eragon. Where the dragon bonds over with a certain human. This elevates their mental state as they mostly feel human emotions like compassion and care for one another.

Right now I don't really know which one is better over the others. They are both pretty generic so in all honesty, if I had time, I'd try to make my own version. However, I got a lot of school stuff for today and tomorrow. So maybe after that i could make some way of dragon rider mechanic.