Lots of destruction magic since im a breton when the dragon is flying. When it is on the ground I will run around in circles around it and hack it with my enchanted sword. I will also roll away/dodge right before it breathes fire. If i'm low on health ill use a powerful companion of mine to dish out some damage while I heal. To make dodging the fire easier, I might use the slow time shout to jump out of the way in epic bullet time style.
I hope dragon fights are gonna be very fun and require tactics.