Simply put:
Weapons = You want Enhanced Effect for dmg
Armor = You want Enhanced Effect (heavy / medium) for defense
Cast/Heal Charms = Enhanced Effect for either Healing or Dmg
Intelligence on items = More Cast / Heal effect
Strength / Dex on items = More dmg ... Note: some weapons are more effective with one or the other except Axes & Battleaxes
Heal Mastery on Items help you with healing if you are a pure healer.
Acc Slot... ONLY Enhanced Effect work for that slot, all other mods are ignored.
Enhanced Effect only works with the item they are on.