Cycle your CDs and keep your eyes on hate. As a healer I want you to be doing your maximum damage, while I do mine.

Shield Oath when it's more effecient (You don't have any CDs and are Mass pulling, since healers will out DPS you by miles.)

On bosses Sword Oath and let the Healers take care of you, so long as you continue to cycle your CDs, after you establish hate with Shield Oath like others have said.

If you have a good ninja, you don't even need to open with shield oath. :]