Also important as tank be it gld or mrd u get the full aggro combo only at higher levels (gld lvl 26/mrd lvl 30) when i leveled those there was a point at level 20-40 you have the groove how to tank lowlevel dungeons then you start the highlevel ones and once you are level 50 and did 3 weeks only highlevel content you loose it again. I usually dont care if i help lowlevels out and loose aggro (even happens to me if I played pally for a bit i start being noobish on war in endgame).

To make your aggro management easier markers 1/2/3 might help you though so you simply combo target 1 keep others with flash and just switch every 2nd or so combo quickly to the other mobs to generate more hate that aoes or heals dont pull off you. This switching target is VERY important try to not forget ^^