Teostra

The fight is fairly simple once you get the hang of it. However, you should keep some things in mind when fighting it.

Attacks

Sweeping fire breath - fairly simple to avoid, just get as close as possible to his face
Embers around Teostra - either move away with dodges or get under him if they are at a fair distance. They blow up once he attacks
Fire aura - fire resistance of 20 helps immensely to negate it, together with fireblight
Fire Nova - just do a superman jump or flash it
Tail sweep - fairly simple to avoid just get under his tail or by the side of his body. This way you can get in some additional hits. to keep up the pressure