MRD is the easiest tank to learn on, get GLA high enough first for flash to make your pulls a bit easier. Than spam Over power a few times. Let your tp build back up. Rinse repeate. Don't do it on bosses however and use your normal

Good skills before your job crystal
Invgorate - DRG's tp restore, good for OP stam
Raging Strikes - ARC damage buff.
Blood for blood - Use this only when you understand tanking and the limits of your healers or pairing CD's to mitigate some of it's effects.

Other than that level the sub jobs for the particular job up to max so that you'll have them when you have to use your soul crystal.

Oh and....

https://www.youtube.com/watch?v=FPAJtvy1uL0