A few tips for the first Guild Raid in global coming from a JP player. I'll skip over the weaknesses of each boss as they are quite easily available and probs have been gone over many times in other guides.

1. Changing starting position is vital. Each map usually have 2 proxi slots that are close to the boss and 5 further slots and your default starting position is always the 5 further slots. Units that have no ap issues should always go into the proxi slots so that they can get in some dmg/debuffs turn 1. Even without mages, swapping units around for better buffs is very important as well.

2. The boss always goes for whichever unit is the 1st unit in team formation if no hate change is involved. This rule overrides the maximize dmg rule. This is what we figured out with a lot of testing on the jp side. Thinking about where to put the boss' target can help you get the boss to a place you want. Diabolos always starts with a single target move that can confuse and you can easily gear up for confusion res if you know who diabolos is always going to go for.

3. Dont be afraid to use off-element. It should be pretty obvious now that the bosses are not created equal. The bosses have different total hp at each round and different mechanics, resulting in different difficulties. In my experience, the difficulty order is Glacial, Kraken, Ramuh, Ifrit and Diabolos. Even Tier 10 Glacial did not survive 5 attacks, so a lot of my guildmates who prepared a fire team had to use it elsewhere and to decent effect. Seymour's slow and ct steal allows fire team to achieve moderate success in Ifrit Diabolos or Ramuh. Dark teams can be used similarly as it boasters two of the strongest CT stealers as well as kain who is one of the few units that can consistently land slows on the bosses. Wind and ice also have pretty good raiding setups. So dont just wait for a specific boss, diversify the bosses you can hit and work with your guild.

4. Turn management.In Guild Raid, one of the most important part is managing turns. Once the boss is in range, most units should avoid moving after attacking to save CTs, making it harder for the boss to get a turn and interrupt your chains. However, you can still make minor adjustment to delay/push forward turn order so that you can get in all the debuffs before chaining or stop a unit without ap from getting a turn. A general experience is to have units that debuffs, then units that hit the dmg cap easier(aka units that do single hits or more base attack) move first, while the units with lower mods or higher hit counts move later. This is something that requires a lot of tuning and you should actively practice around these if you want to gain better scores.

5. Careful when attacking simultaneously. The way scoring for simultaneous attacks work is that the system records your dmg dealt and applies it to the boss' remaining hp pool once you leave the battle. The boss does not update its remaining hp mid battle. If the boss has less remaining hp that the amount you dealt when you come out, the extra dmg is removed. So, especially when the boss is close to dying, avoid attacking when other guildmates are in battle to avoid dmg overflow.

6. Have guildmates bail you out. With the scoring mechanic mentioned in 5. There is a way to use it to your advantage. If you finished a boss when the boss is already dead during your battle, you get your attack attempt refunded. Therefore, if the boss is on low hp and a run goes terribly wrong, like if you forgot to set initial positions, brought the wrong team or got RNG'd, you can wait inside the battle and call for your guildmates to finish the battle and rescue your attack attempt.