Hi, I am just now learning to tank as a marauder. I am only level 24, and here is what I've learned so far:

Macros:

/macroicon "heavy swing"
/ac "heavy swing"
/wait 2.5
/ac "skull sunder"

This macro attacks with heavy swing, then AUTOMATICALLY attacks with skull sunder 2.5 seconds later. You can cancel skull sunder and hit target with Maim by simply pressing the maim hotkey when the GCD is reset (before the macro hits with skull sunder).
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/macroicon "bloodbath"
/ac "Bloodbath" <t>
/ac "Foresight" <t>

*** This gives you a great buff string for tight spots in fights.

/macroicon "tomahawk"
/marking attack1
/ac "tomahawk"

This marks your first target and attacks it with tomahawk.

TACTICS

I go in with tomahawk, then (while I am MRD) Straight Shot for increased crit (while at the same time I run through the mobs and jump+mouse turn so all mobs are facing away from party), then Overpower, then Heavy Swing, then Maim, then Fracture, then heavy swing macro.

While a lot of emnity building will be situational, and my strategy assumes people will pay attention and not try to destroy my efforts, this strategy is working quite well for me.

The number one thing I think you need to remember as a tank is don't be afraid to speak up. Protect your healer. Defend your healer. Most of the time, things go wrong because of DPS. Sorry, guys, it's true. Y'all get trigger happy and start attacking chandeliers on the ceiling and generally don't pay too much attention. I say this as a healer main, DPS 2nd class, and now tank. It's not always true, but generally.

You control the run. Yeah, we all work as a team, but the tank has to manage a lot and be on his/her feet when something goes wrong. Don't be afraid to lead that party to success. And ALWAYS be helpful. If you see something someone could do a little better (or correctly), feel free and politely offer them your view. It's up to them to take it or leave it.

My first few runs were scary. I simply told the party I was learning to tank and to please be patient. Mostly, people have been good about it. Then I got to a point where I felt comfortable doing chain pulls. I simply watch my healer's mana and any party chat, and just go with the flow.

One thing's for sure: while I have always gotten steady commendations in my BRD/WHM roles in parties, I keep getting sets of 3 as a tank. So, there's that.

Happy tanking!!!!