Here's what you need for promyvion:
- Intelligent preparations. If the boss can sleep you, you bring poison potions, doesn't matter if you're a mage and expect the melees to keep it away from you. If you're a mage or main/sub NIN, you bring echo drops in case of AOE silence. If you're a melee, you bring a few Hi-Potions for when you need healing and you can bloody well see that the WHM with 20 MP isn't gonna be able to toss a Cure III on you. You might not end up using all these, but just as a tip ... you can *sell* stuff on the Auction House too.
- Well-behaved party members who not only listen to instructions but follow them (or speak outright in Jeuno, if they choose not to follow them, rather than only mentioning the fact once you get to the Spire). This also includes a bit of common sense stuff such as, I dunno, not going afk halfway through Promyvion? Supposedly common sense anyway ... considering that mid-Promyvion afks happens quite often, it must not be common sense.
- A team mentality among the group travelling through Promyvion. This is the most important thing. You make sure, in particular, that there is always at least one WHM alive, because guess what - no other job can Raise at level 30, and Reraise isn't until level 33. And the other thing you make particularly sure of:
- *YOU DO NOT ENTER A MEMORY STREAM UNTIL ALL THE STRAYS ARE DEAD OR OTHERWISE OCCUPIED* (i.e. sleeping or distracted by a SMN avatar or a volunteer martyr who's already completed that promyvion - that last, only assuming you can beat the boss without 'em). The things take a whopping 3 minutes to disappear, if you have 2+ parties you *will* have time to kill off all the strays, even on the third and final portal, but not if 80% of the alliance jumps through the portal as soon as it opens (or whenever their panic hits about maybe not getting through in time).
Do not go through the portal until it's safe for everyone to do so. Promyvion is not "every man for himself", because if your team doesn't get through the portal too, guess what - you're screwed. It's better to fail to get through the portal and have to go open another one, than it is to abandon your team members. That sort of jackass attitude is far and away the #1 cause of promyvion failure. (#2 is dying to the boss through some combination of poor preparations and poor strategy, and #3 is just plain bad luck when you do everything right but still fail.)
- The ability to follow instructions from the leader (you do, of course, need a good leader for this one to work). If they say to buy something, buy it. If they say to stop attacking the memory receptacle so that some strays can be cleared out, stop attacking. If they say to stop moving, stop. If they say to run, run. And if they say to go through the portal and leave people behind while they're still fending off strays, they're an idiot and should henceforth be ignored. Assuming the leader is not an idiot, of course, do not assume that you know better than they do. Argue back if you like, to try to change their mind, but don't simply ignore them.
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And ultimately ... this is why promyvion failures are so rampant. Because people can't follow instructions, can't use common sense, and abandon their teammates rather than working as a group. One or two bad apples like this might not ruin a promyvion ... but if too large a percentage of your group is similarly incompetent, it *will* result in failure.
Be prepared with items (and don't volunteer for a Promyvion if you are unable to afford a few potions). Have an intelligent leader and follow their instructions. But most importantly, play as a *team*.
Specific job combos are good, 2-hours are good, animas are very good (another tip: if you're interested in Promyvion, go farm up an anima *in advance*). But ultimately what will really matter is the paragraph above. If you can't do that ... you will have a very difficult time succeeding, if you can succeed at all. That's all the more there is to it, and that will always always be an issue unless the level-cap on promyvion is removed so that it's possible to walk through there aggro-free.