This type of set is used to cut down the damage received so each attack hurts less. It will not work in all situations and some areas may require a different strategy such as a damage avoidance tank set. The general consensus is that 800+ ac is considered decent enough for most areas, while with some effort 900+ is obtainable and used by a few elite tankers.
Consecrate, which replaced the enchant armor spell, is a cleric skill that trades deity favor to imbue objects with extra protections, for it to work the item must be of type armor, have no bonus affects, have no light flag and have no spells attached. The favor cost of consecrete varies depending on existing standing with a god and how much protection is granted. If a player has high standing then less favor will be used. Consecrated objects gradually lose their potency over time so are often kept on a storage char when not in use.
Dark steel pieces for fingers, wrist, neck, waist can be found in both the Village of Egmondville and the Village of Newtonia, there is also a ac85 tower shield which can be traded by handing a newt shopkeeper three darksteel shields from the a two-headed troll in the warehouse.