Your main necklace 99% of the time is Lilith's Soul Necklace for the Mental Attack which is your most important stat. It's the only necklace giving Mental Attack and Defense. For Olympiad you can use Blessed Valakas' Necklace for the extra damage but only versus certain matchups, as for the Frintezza's Soul Necklace - only versus Tyrrs. Earrings
You need 3 earrings, 1 that you will have all the time, and 2 for switch.
Blessed Antharas' Earring you should always have it. Gives you a huge defense, and it one of two best earrings ingame for the Mental Attack.