Effects attached to items are applied to creatures as the item is equipped. However, when the effect stack is loaded in its entirety (e.g. loading a save game, moving between areas), effects are applied in the following order:

1. Helm slot
2. Armor slot
3. Left Hand (Shield or second weapon) slot
4. Bracer slot
5. Right Hand Ring slot
6. Left Hand Ring slot
7. Amulet slot
8. Belt slot
9. Boot slot
10. Cloak slot
11. Right Hand (primary or two-handed weapon) slot
12. Magical Weapon (harm, meteors, etc) slot
13. Spell Effect (first active spell cast)
14. Spell Effect (second active spell cast)
15. ...

Spell power, level, and duration make no difference to the effect application order. Fixed and cumulative effects generally work as expected, however for some effects the engine calculates the new (fixed) base stat and then appends all cumulative modifiers to it.