Don't fail to move the crystal with some class that can do damage while moving, like, oh, NIN mebbe.
Don't target tanks.
Don't fail to steal all potions in the area to prevent that almost dead guy from getting their health back to 100% before they murder you.
Don't fail to avoid environmental damage.
Focus fire with call-outs.

These are complex strategies that even at Diamond/Crystal rank still elude some of my allies.