I sort of understand your post, but I think I may have misconstrued some of it, so feel free to correct me:
If you're the tank, worry about the boss above all else. If the boss starts going for other party members, you're probably going to wipe - especially if it's the healer. They can take two, maybe three (if you're really lucky) hits before they go down. From there, in terms of adds, I suggest trying to get as many as you can, but it's not necessary in lower-level dungeons since most DDs can handle them if it's just 1v1. If your party members have 3-4 MoBs on them, you need to pick up the pace and start getting the adds' aggro. I personally try to take every MoB's aggro without losing that of the boss as soon as I see them.
As a tank, the order in which you kill MoBs doesn't matter as much as making sure that you keep their aggro. Marking allows the DDs to focus which MoB to kill, but again, in low-level dungeons, I haven't run into a case where marking MoBs in a boss fight was essential - usually there was only one or two MoBs (except for Halatali, but those MoBs died in one or two hits so it didn't matter).
Long story short: In low-level dungeons, try to aggro the adds whenever you can, but don't lose the boss.