I did alot of high level raids in EQ, and some of the strats from that game can be applied to low level parties, even in FFXI.
1. Share the Healing, if you have any backup healer like a rdm or whm sub, they should throw out the occasional heal, this helps the whm's since they don't have to do a heal and get more hate. In EQ on raids with super-mobs you would have a main tank maybe doing 50 dps, while a dragon was doing 250dps, so how does the cleric manage to heal without getting eaten, easy, there is about 10 clerics that need to do 25 healing per second (hps), as you can see, that is half as much hate, add tuant and patch heals in and aggro control should be easy. This can be the same as with one tank and two whm, tanks does say 50dps, mob does 75dps, two whm's only need to do 38hps.
2. Build Aggro, high damage should not come at the front end of a battle, in EQ on a dragon the tank would solo (with heals) for as much as 30 seconds. Same should apply in FFXI, the tank should get in a few hits and a provoke before melees and debuffers attack. Not until the mob is down 75%, even 50% should nukes even come in, in EQ you might not nuke until as low as 10%!).
3. Position, this is extremely important, learn positioning, keep the tank-types to the outside and the mage/damage dealers to the inside, if anything adds, it does so to a tank. From level 1-30, All tanks that may gain aggro should be on one side, this way they can see the mob has aggro'd on someone it shouldn't when it turns. If the mob moves, make sure you don't just follow it, set up position again! Keeping tanks on one side also helps thieves sneak attack since the mob won't be moving back and forth, this is combat, not a tea dance. From level 30+, if you have a thief you will want to utilize Trick Attack, and you will need tanks on either side, you local thief can easily explain this to you as such:
Thief-->Tank A-->Mob--><--Tank B
When they do their trick attack with sneak and viper bite they will rip as much as 25-50% of the mob out of its *** and make the mob think the warrior they are hiding behind did it providing that warrior with serious aggro, if this is done near the begining of a fight Tank A can easily keep aggro for whatever is left. The important thing is that the thief MUST strike the enemies back for it to work properly, so position is absolutely key, anyone that doesn't understand this doesn't deserve the advantages of having a thief in party.
4. Crowd Control, sometimes you get additional mobs (adds), if you have two tanks, one tank should take a mob and solo tank it instead of having the main warrior have to provoke two mobs, if a mage can sleep the mob that is even better.
5. Apply Debuffs, each debuff is important, it may seem a small thing if you slow the enemy by 10%, but that is 10% less damage the healer gains aggro from when healing, and if you haste your party by 10% that is 10% more hate the main tank generates, that is a 20% difference right there, and that is major. In EQ if you didn't slow somethings, it pretty much wasn't killable, but you could slow it 60% and haste your warriors by 50% plus.
6. Know your Stomping Grounds, do research, take a few minutes to learn what aggros, what links, and what doesn't, what mobs have high defenses, low damage, elemental weaknesses, good loot. Buy all the maps you can, learn unmapped areas and details not shown on maps, learn how to use <pos> and compass direction.
7. Follow Directions, your leader is the leader for a reason, the leader gives the orders, and you follow them, even if you don't like them. When he moves (unless he is the puller or tells you to stay at camp), you move with him, don't use auto-follow, don't dilly-dally and smell the flowers, stay close to him, if you lose him immediately say, "Wait, lost ya, come back." Don't move unless you will aggro something, the worst thing you can do it go up the wrong canyon and get eaten by the Superbeast. If you leader tells you to "RUN!!1!1!!", you hual ***, don't try to save someone, they are dying so you don't and is likely about to run as well. The whm or warrior shouldn't call run, only the leader, they should be informing the leader if their is a problem, like "Out of Mana, Cannot Heal!", then the leader makes the call and the tank takes the death for the team, that is a tanks job, and they should be used to it. In EQ there were monsters that could instantly-kill (no chance to heal or resist, just death!) a person every 30 or so seconds, and you always have one person aggro it and take the first death, it was an honor, not a burden.
8. Respect Each Other, drama happens, but hopefully not often, I seen it all the time, people just can't accept they are wrong sometimes, if someone tries to tell you how to do your job, they are only trying to help, if you think they are wrong, explain why you do what you do, and ask them why they think it is wrong. They should explain, and somewhere along the line of logic someone will realize they are wrong, you should be willing to admit you are wrong, and learn what is right, this is a 200% increse in player skill right there. I truly respect the player that dies and says, "Sorry guys, I didn't do suchandsuch and got killed, I won't do it again." I would much rather have that then, "WTF, why didn't you heal and voke stupid party! ***** you guys!'/disband"
These are just a few things I have learned that are basic rules for combat, if you don't understand and follow at least these you are effectively a 'bad player' no matter how many levels you have or what uber gear you got, strategy is 99% of the game.