Usually, you don't want to try; one gas breath from a full-strength AMHD does 693 damage, with no resistance. If you can get to speed 3 (one permanent speed item, and either another permanent speed item or a haste self spell or staff), you can try this technique. First, create (or find in a maze room) a wall with one open space on all four sides. . .#. . Stand on one side, with the dragon on the other side. When the dragon moves adjacent to you, attack it once, and then hide behind the pillar. The dragon can't see you, so it won't breathe, and will instead chase you to another side. Now attack once, and hide again, and so on until the dragon is finished.