6 years of tanking so i will give my take on this.
1. First rule, Know your class inside and out. Without this knowledge you will fail the following rules below.
2. second rule, know how to grab agro and maintain it. The softies in your group will love ya for your efforts. Know how to rescue them when they get over zealous on DPS...(cough) wizards.
3. Third rule, I like to call it situational awareness. When fighting a mob you not only have to worry about agro but the roamers also that is nearby. The group will listen but you must be the leader for the group when it comes to combat.
4. fourth rule, Know how to pull wether it be by proxitimy agro, bow, taunt pulling or jsut plain whack the mob in the behind.
5. fifth rule, making sure your gear is up to par accordance to your level. if your still wearing lvl15 armor and fighting lvl30 mobs.... you are gonna be hurtin in morning :P.
6. Sixth rule, Lastly ....make a battlecry emote! ....cmon you gotta make one of these its kinda of calling card
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Seriously though, these rules i live by when I am tanking. Just keep in mind taht Raid tanking has a few rules beside these one I had stated. Also if the group has advice to offer wether it be about the mobs,skills or whatever ...listen to them. You never know what you can learn from others. I am not saying you have to listen to them ....sometimes two minds are better then one :P.