Profile of A Great Tank

Below is a list of invaluable attributes of a great tank:

• A great tank always has top aggro on all targets that they are assigned to tank, and not on any other targets.
• A great tank has excellent reaction time in picking up new mobs, before these mobs attack other raid members.
• A great tank has excellent reaction time on taunting back targets that they lose aggro of (which happens to everyone at one time or another).
• A great tank is intimately familiar with all the fight mechanics, and because of this, knows when and where to move, and when and how to use their defensive (and sometimes offensive) cooldowns.
• A great tank understands the various positional requirements of (especially melee) DPS players, and does a good job at minimizing their movement and downtime.
• A great tank has the qualities of a leader, and is not shy to step up and take control of the group.
• In addition to this, as tanks are the drivers of the party or raid group, a tank who is able to set a fast pace will make the dungeon or raid go extremely smoothly and quickly.

From Tanking Guide on Icy Veins (written for WOW players)