The most important part of this fight for anyone in it is to know the cycle of the fight. For DPS this is an understanding of when they need to take off their blinders, for healers it's when to throw up mitigations.
No, you can't get enough Lightning Resistance to make Imdugud a joke: I'm sorry.
Modulate your rotations such that you keep your big cannons for Critical Rip. Specific rotation for Paladin given below.
Paladin rotations for Imdugud and Adds
Critical Rip #1 should be responded to with Rampart, if you encounter a second before Adds phase, the second should be responded to by Sentinel.
The Adds are responded to thusly: Begin with Foresight and Convalessence. This gives your healer a real chance to do good work. Once those wear out you'll move to Bulwark and Awareness as a stop gap.
When you return to deal with Imdugud again, it's back to Rampart and Sentinel yet again. This time Critical Rip comes after Wild Charge. Blow your cooldown either to eat Wild Charge or to eat Critical Rip. It goes Rampart > Sentinel > Rampart > Hallowed Ground. If you somehow reach Hallowed Ground you will more than likely be hitting soft enrage.
Warrior rotations for Imdugud
You can respond to Heat Lightning/Wild Charge by using Holmgang to eat the charge, you will take considerable damage, but survive. This can be used to avoid one messy tank swap.
White Mage, you are responsible for the general health of the party. You must perform medica II's after each Wild Charge and must work to keep stone skins up on you, the off tank, and your Scholar as best as you are able. Prey is no fun.
Scholar, it falls on you to deal with Prey. Work out your timing, and be mindful of when it appears during the fight's rotations. Swiftcast > Adlo i your friend here.
White Mage, make sure after each Electric Burst you've got Medica II's up on everyone and regen on the main tank. The value of Regen hits its peak here, helping you mitigate auto attacks from Imdugud.
Always be mindful of how to safely arrive at the charge zone. Your pathway changes dependent on distance and obstacles. For the purposes of handling it always remember that you can technically stand safely inside Imdugud while you're moving through if you are fast enough.
The real DPS checks are happening during the Adds phase. If you are on about 86% or 56% save any oGCD skills you have for after adds pop.