Advice for being a tank

[Scotty_ffgamer]

I was just curious if anyone could give advice for someone like me who has always been pretty bad at MMOs and has only a vague knowledge of what each role should be doing. I'm currently a gladiator, and I have just recently reached Sastasha. I've only ever played as a DPS before back when I played WoW as a kid. So yeah, how do I be a good tank?

Also related, would anyone from the Fat Chocobos be willing to run Sastasha with me sometime to help me get my feet wet in the tank role?

Edit: This could also just be an advice thread for any of the roles to expand discussion.