As title states, please pay attention to the party.
I know that when I tank, there are a few things I do before we even really start. Personally, I think tanks really need to follow all of these up to #8. At a minimum. First 7 I do in order.
1) Check classes. No AoE DPS? No real point rushing (DoTs only last so long so rushing too much will only put unnecessary burden on the party)). No bard, make sure the healer has enough MP. Scholar in a low level dungeon? Prepare for debuffs that won't get removed. etc.
2) Check gear. Especially for the healer, but also for other classes. This lets me know what to expect (so I pull the right amount) and what NOT to roll for. (I do this for all classes, not just tank-since if I have level 90 gear and the other player has level 15 gear, I shouldn't be needing on the level 30 gear when the other player clearly needs it more than I do. Heck, I often will ask before I even greed if I know I already have gear just as good or better).
3) Check for new players (usually there is a message, but I also like to ask since it sometimes doesn't show up)
4) Wait for buffs.
5) Look for any requests (speed run, fast run, do multiple groups, keep it slow, full run, etc.)
6) /readycheck
7) Make sure the party is following me!
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Once we get into things, there are a few things I pay attention to. At least pay attention to 8!
8) Aggro. Make sure I'm holding aggro and watch any enemies I'm losing aggro to.
9) Targeting lines. Pretty simple, I watch what my party is targeting.
Seems like too much work for a tank? Healers have to do just as much or more. See #13.
10) Disconnections or sudden afk state. People disconnect or go afk and this can happen at any time for a good number of reasons.
For this reason, I generally stick with normal pulls rather than an excessive pull. And I never purposefully overpull. I define normal pulls as the party can handle comfortably. I define excessive pull as pulls the party can just barely handle if they push themselves. I define overpull as the party will wipe unless RNG decides to favor the party (aka. a miracle).
For this reason, I generally save an emergency card for "when things go wrong, I have a backup plan and can go all out for a few seconds to make up for whatever went wrong." Some people might not agree, but I like having it.
11) My own exhaustion level. Am I starting to get fatigued from playing the same mission over and over? Is my morale getting low? Am I starting to fall asleep? Depending on my answers, I'll change my tanking slightly to make up for that. Which is why I've tanked in my sleep before.
12) My party's exhaustion levels. Same as above except for my party. Are my party members showing signs of fatigue? If so, I will change my tanking to make up for that.
13) Pretty much everything I pay attention to as a healer. When I play a healer, I'm watching HP bars, enemy enmity meters, targeting lines, enmity on me, buffs and debuffs on party members, buffs and debuffs on enemies, current position of allies and enemies, my own MP, party member's MPs, to some extent, party members (tank specifically) tp (based on regen and skill usage), aoe zones, skill load times (specifically for enemies), allies within those aoe zones that won't make it out, debuffs caused by those aoe zones (though no point pre-casting esuna since it sometimes won't remove the debuff if you start the cast before the debuff even if the cast won't finish until after the debuff is placed-probably to prevent people from casting esuna as a counter to silence), damage caused by those aoe zones, incoming enemies, skill cooldowns, etc. And I'm not on the PC so I don't have this FFXIV-APP people keep talking about having. I am still struggling a bit with 8/24 player missions since I don't do them as often as 4 player missions.
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For anyone going: hahaha, your tank classes are too nub to give us your opinion. In addition to tanking with my tank classes, I've tanked as a THM, as an ARC/Summoner, as a SCH, and even my WHM. Obviously not for end game dungeons (even I kite instead of tanking)