"As with all dragons, an Anti-dragon/Dragonfire shield and an optional anti-fire potion are essential when fighting them. Without the shield, you can be hit extremely hard by the dragon's firebreath, while the anti-fire potion will only provide added protection. An anti-fire potion alone will NOT provide the needed protection.
Dragons will use both a melee and dragonfire attack while in melee range, but will only use a ranged dragonfire attack while the player is out of melee range. Using both a Anti-dragon/Dragonfire shield and an anti-fire potion and using range or magic to kill them will mean you take no damage at all. Using a Rune Crossbow along with either mithril or stronger bolts as well as using fire spells (such as Bolt or higher) makes killing Iron dragons a lot easier."