Try waiting behind left pillar by the door until the dragon is calm. Get the scales in the middle of the spine. Hide again. Read the book and mix the blood you found in his room with the dragon scales. Change the dragon to Amdusias. Get him moving with a few arrow shots. Hide behind the left pillar again so his arrows can't get you and he draws his sword. Once his sword is drawn you can kill him with a big old sword.
