Neverwinter Nights armor
Armor class (AC) is primarily used to oppose attack bonus (AB) which is the primary form of attack of most characters, player or otherwise, encountered in Neverwinter Nights. Because of the way AC is used, having an AC that is insufficient, even if only by five or ten points, is not significantly better or worse in combat than having a poor AC. For example, against an attack bonus of 60, a defender with a 60 AC is only marginally better off than one with a 30 AC, and even a defender with a 70 AC is quite vulnerable. Thus, one's armor class is only relevant if it is significantly higher than the attacker's attack bonus; specifically, an AC that is 20 higher than the attack bonus is required to be safe. This results in there being two approaches to avoiding attacks: one must either devote considerable effort to having an AC that is completely out of reach of the attacker (which requires knowing the attack bonus of the opponent with some reliability) or simply abandoning the character's AC and focusing on resisting the effects of the attack. Each method has its own strategies.
Investigate the environment
First, determine the likely attack bonus of your opponent. This step is crucial; the difference between being 15 above the opponent's attack bonus and being 20 above is often the difference between life and death for an AC build. As an example, we can use the 60 attack bonus used above, which is a value well within reach on virtually any PvP server. Once the attack bonus is known, add 20 to it, or 25 if the value is only estimated. That is the AC your character must reach to be safe. Now we must go about reaching that armor class.