The dragon rider image idea came from wanting to have a "domesticated" dragon and a close-up of it's owner without losing the dragon's sense of scale. One of the more intriguing aspects of the "Game of Thrones" series for me, is the idea that the general populace thought the Targaryens simply ordered the dragons around. We keep getting glimpses of that actually not being the case. That it would be closer to a trained tiger begrudgingly (we don't know why yet) obeyed. I suspect it has something to do with the horn that was found by the pirate in the "Iron Islands" thread that incinerates people who blow it, but we shall see.
I spent a good deal of time trying to get the sun just right and if you look carefully, you can see it's highlights on the dragon armor, its back, and its snout. The 'rider' also took quite a lot of tweaking to get right. I wanted her hair to catch the red sun and look like fire or flames and was happy with the result.
Finally I added the mountains and water to again give the scene some sense of scale as well as set the mood for the type of land they are in. Since there is snow on the ground, and the dragon is in armor, are they on the way to battle? I thought it implied a sense of departure and heading out of the flame/warmth into a cold & barren landscape. You'll noticed in many of my images, a color shift from light to dark as you look from one side to the other. This is always very intentional and I love how light and color can be manipulated like that when working in this medium.