If your warrior is attacking the enemy with their weapons, and employing her Taunt abilities regularly, then she'll be able to maintain the enemy's attention regardless of the amount of damage you're dealing. In a reasonable manner that is, of course. If you're a level 30 mage WoTLK Gold, and you're in a battle with an ally of level 25. you're likely to be able to constantly be hammered.
Additionally, it is difficult for warriors to taunt several opponents at the same time. If there are two enemies in front of her, and is only able and able to take on only one, one of them will probably slide away and attack the initial player in the group that causes the damage. So, you would not like blasting damage spells that target areas of effect unless you're certain you'll be able to fight one of your foes in the event that it ends up landing at you.
One of the lesser-known causes of aggression, however it's healing. The mobs aren't happy when someone is healed and they're more likely to head straight to the healer even if they've not been assaulted. Even if they're being targeted and beaten by the warrior, mobs can still be jolted out by powerful healing spells like the priest's Great Heal. Because of this, many healing classes opt to weaker healing spells which can be performed quickly and often like Lesser Heal or Flash Heal which will result in lesser aggro but less efficacy, yet giving you the option of a massive healing in the event of an emergency. Regeneration spells such as Renew or Rejuvenation may get the least amount of ado about them of the bunch, as they spread their healing benefits across a lengthy amount of time.
There's nothing more unpleasant than being a party host to an unprofessional, which is why you'll be sure you treat every person that you come across with respect. This is typically an issue with loot where parties are often to a standoff over who should get the items dropped. The game offers a variety of options to loot that makes the problem of ninja looting in the beta (where players would steal items to buy WoTLK Classic Gold sell in the event that other players could more profit from the items) is a thing of the past, however there's still plenty items that fall under the threshold for the lottery-based looting system which a lot of groups employ.