Before we get started, lets weigh the pros and cons of being a shaman tank. Actually, scratch that. Let's just look at the pros since there are no cons.
1. The ladies love a shaman tank
2. A complete reconstruction of the enhancement spec is EXACTLY what we need right now.
3. You can finally use rockbitter all the time in dungeons without being called a baddy.
4. You can pull groups of mobs without getting vote kicked.
5. Even if you don't want to be a shaman tank, it lowers your DPS if you feel you are doing too much.
6. Fast dungeon queues. (Even faster than other tanking specs)
7. Shaman tanking is what makes magnets work.
Now that I've completely sold you, its time to get down to business. Welcome to the world of tanking! You may have mixed feelings right now. You may be scared, embarrassed, or even doubtful. Whatever you may feel, always remember to doubt your feelings when it comes to shaman tanking. As a beginner, logic is your worst enemy. It will take a while for your shaman instincts to adjust to this new concept.
Another thing to keep in mind while being a shaman tank, is to take what people say the opposite way. People will be so awestruck by your skills, that they will sometimes say things the opposite of what they really mean. (If someone tells you to go kill yourself, it means they appreciate your existance. If someone tells you that you suck, take it as a compliment to your superior skills. If someone tells you to let someone else tank, they are actually cheering for you to keep up the good work.)
-Gathering The Essentials-
First, you are going to want to grab a tanking shield and a tanking main hand weapon. You can find these in an assortment of 5 man dungeons. Simply roll need on the first tanking shield or weapon that drops. The tank that is in the group with you at the time may begin to call you derogatory terms or even attempt to vote kick you. However, you have to remember to keep your head in the game. Calmly explain to the current tank that you are using it to become a shaman tank. He should understand, and will apologize for jumping to the preposterous conclusion that you are a ninja. If he does not apologize, he may leave the group and allow you to tank because he is so embarrassed for doubting a shaman, that he just can't continue tanking.
You may also use 2h weapons to tank. Death knights, Warriors, and Retribution Paladins are most generous when it comes to allowing shaman tank enthusiasts to roll need on 2 handed weapons. They are also very humble, and will pretend to react in harsh ways just so people don't think too highly of their generous nature.
-Putting Together a Team-
As a shaman tank, you are superior to all the other tanking specs. You need a group worthy of your presence. However, finding worthy group members is no easy task. They lurk in the shadows, secretly waiting for a shaman tank like you to accept them into your group. Check world of logs or your local trade chat for the absolute worst players. Worthy group members for a shaman tank usually disguise their power by pretending to suck. Any normal player will instantly reject your offer to tank for them, because they know that they won't be able to survive the severely high levels of awesomeness radiating from you.
There is no specific priority system for a shaman tank. That's one of the nice things about shaman tanking. You will get the same results no matter what priority system you use. So mix it up! Be creative!
-Your First Dungeon-
It's time to step into your first dungeon. You may want to grab a healthstone and a few potions before you do this. You may also want to choose a paladin as your healer, because of Lay On Hands. Keep in mind that you may wipe more than you would if someone else was tanking. The reason for this is because the game senses your superior skill level, and raises the difficulty of the dungeon.
I recommend picking up the following talents, to get the most out of your tanking experience.
-Gemming and Reforging-
Have any suggestions? Feel free to add them. Being a tank, I don't normally accept suggestions from others, but I will make an exception for my fellow shaman.