How to tank, a lesson in 3 parts
Part the first: Be a Ranger or a Monk (or both).
Part the second: Get out your bow and engage the multi-shot (note - this is different than multi-pass, even though both are fun to say in Leelo's accent from the 5th Element). Get the enemy's aggro (i.e. his attention will be focused on you because you will have done more damage to it than anyone else since you can shoot it before the melee get in range and because you're shooting several arrows per attack).
Part the third: Run away from the melee types in large, looping circles in order to keep them from engaging with the target. This will prevent them from taking damage since they will be chasing the enemy and attacking from behind and as long as you stay out of your target's melee range, you will also take minimal damage from the enemy that you are tanking. Plus, this has an extra benefit for all of the melee characters in the party who get to enjoy the extra challenge of hitting that moving target. Since so many quests in DDO are so very easy, players will enjoy and appreciate that extra challenge.