Honestly, if you're hitting the same target as the tank and stealing enmity, there's likely a problem with the tank. They're either undergeared, or are not using their enmity combo (Fast Blade + Savage Blade, or Heavy Swing + Skull Sunder). That said, debuffs are a way to contribute to the party while minimizing your enmity. You can use Feint to inflict slow (Use it again when slow wears off) for example. If you get Quelling Strikes from archer, you can reduce the enmity of actions while it's up. Damage Over Time (DoT) abilities, however, are not effective for lowering enmity as you will still get enmity for the damage they deal, like any other weaponskill. They are effective for damage though (Phlebotomize, from your level 30 class quest, is essentially a 320 potency attack)