You need an anti-dragon shield to defend against their fire attacks (which can hit up to 610) or they will hit some serious damage on you. The blue dragon's melee attack hits up to 100.
Weak against ranged attacks and, unlike other dragons, weak against magic. For melee, it is weak against stab attacks, but high level weapons such as the abyssal whip is just as effective. When using magic or range, try to find a safe spot to attack it from.