Priest Lead Guide
Here is a rundown of the jobs that a priest lead should assign in MC. If your raid is really strong you might not need this level of preperation, but this should be helpfull to those that find themselves in a priest lead role and are unsure of what they need to do.
Start of the Raid
At the start you want to come up with 3 healers for both the Main Tank and the Offtank. These healers can communicate with each other as they need to take breaks so that some can drink while the others heal. This is easy to decide if you have 6 priests, just split them up 3/3. If you have less priests, assign some druids or shaman to help.
Also at the start of the raid make sure someone has their eye on the hunters, a priest or shaman is best for their faster casting heals. This person could also be assigned to a MT/OT, or just be on spot healing as well. Typically when watching the hunters you are only busy for the first few seconds of the fight, and the rest of them time you can fill another healing role.
Remind Priests to dispel the Firelord silence and to clear debuffs when a corehound dies. As far as buffing goes we do not normally assign buffers, and people should just watch buffs and buff those that need them quickly.
Lucifron
For Lucifron all the priests will be in for healing at the start. You should have at the least 4 active healers (not counting the dispeller). If you don't have enough priests recruit a shaman or druid. One priest should be assigned to dispels on those that need it, prioritizing healers and the tank. Call a switch to shamans/druids if the priests need a break after the adds go down. Remember to shadow buff the raid.
Magmadar
Use your MT/OT healers as Rotation 1/Rotation 2. Call switches as they are needed.
Gehennes
The group lead should have the priests split into seperate groups with some support. Those groups should stay together, but spread out apart from the other groups. If needed the priests in each group can set up a small healing rotation between themselves. You should have 6 main tank healers in 3 groups, each with a decurser. Remember to shadow buff the raid.
Garr
You can use your MT/OT healing rotation for the main tank just like on magmadar. The second rotation can help with healing the off tanks at the start and should still have enough time to regen some mana before being called in. Other healers should be assigned by the group lead, healing the offtank in their group.
Sulfuron
The group lead will assign healers. There will be a MT heal group that is normally made up of shaman/druids. Also each offtank will have a Shaman/Druid healer and a priest to Dispel. Shouldn't be any special jobs to assign here.
Golemagg
Like on Magmadar use your MT/OT healers as a rotation on the MT. Group lead will assign the healers for the offtanks, normally druids and shaman.
Majordomo The group lead will assign healers. Heal the tank in your group. Remember to get those shadow buffs up to help with the priests.
Ragnaros The group lead will split the healers into 2 groups. There are no rotations, but each group will stand in a seperate spot. Assign each group to one of the healing spots if the group lead hasn't done so.