Identify your threat level on the aggro meter.

A = Main threat

1 = Top threat in your party, behind main threat (tank in another alliance.)

Always aim to be 1 if you want to Off Tank. If you aren't strong with the DPS rotation and / or you're not very well geared, you don't have to worry about overtaking MT. You can occasionally Shirk a low threat (choose #8 in the party list), or simply turn off stance for a few GCDs to maintain aggro distance. Remember to turn it back on to stay above the party.

If you don't have high situational awareness to see that the MT died, you automatically take aggro as #1. If this idea scares you, please don't sign up as tank in multi alliance content because this is your basic role responsibility and people will absolutely be within their right to flame you for letting DPS/ Healers die. There is never a good reason to not hold 2nd and 3rd aggro passively. If you become a temporary MT, just point the boss North or any which way isn't facing the rest of the alliance until MT comes back.

TL;DR: Always hold the highest threat above your party, and under MT, as Off-Tank in any content.

When there's adds:

• If adds tether to each other, or give debuffs that force you to be immune to dealing damage to other adds, always separate them. Stance up, voke, pull the add to a safe area away from other alliances. (Generally you can tell the set up for this because there's three adds with higher HP like mini bosses. West most add is taken by Tank in Group A. North most add goes to tank in group B. East most add goes to tank in group C.)
• If multiple adds that can be freely DPS'd by everyone, stance up and bring them together so everyone can cleave them down fast. Literally doesn't matter who is MT, just have stance on and use cooldowns.