Here goes as a starter for 10.
Lucifron
Lucifron is your first MC boss. He has two guards, whom you'll need to kill first.
Here's the general outline of the fight.
Your main tank and a support crew hold Lucifron up the slope, out of range of the main raid. A second tank holds one of the guards in place near the main raid, while a third tank pulls the remaining guard down to be killed.
The guards will sometimes mind-control a player. Dispell it. Otherwise, they're not hard. The raid kills the first guard, then the off-tanked one, then runs up to pile on Lucifron.
Lucifron has two abilities of note: a Curse that doubles the mana/energy/rage cost of abilities, and an AoE debuff called Impending Doom. The debuff is pretty much Call of the Grave, doing 2000 damage after 10 seconds. Lucifron's Curse might not sound nasty at first, but it will cripple your raid if you leave it there.
The curse must be removed from your healers immediately, or they'll run out of mana. You can leave it on your meleers without much worry, though you'll probably also want to decurse your main tank. And of course removing Impending Doom will give your healers a break and keep more people alive. Support roles are just as important as DPS.
Magmadar
This is almost a straight, boring tank-the-boss-while-dps-kills-it fight. The one twist is that periodically Magmadar will cast an AoE fear. CT_RaidAssist will give you a warning of the upcoming fear, so your meleers can get away from Magmadar.
You want to keep your main tank un-feared, and also the healers for your main tank.
Warriors have Berserker Rage. They can stance-dance to pop that ability right before the AoE fear times in.
CT_RaidAssist will give you the 5 second warning on incoming fear. Healers should pop HoTs onto the tank to help him through the transition, since he'll be taking much more damage while he's in Berserk stance than he did in Defensive stance.
It might help to have a healer rotation, one group in while the other group stays out of fear range and meds up. Swap after each AoE fear cast.
The tranquilizing shots suppress Magmadar's frenzy mode. Hunters with the shot ability should take turns cooling him down. He does a lot more damage to the tank while in frenzy mode, which can strain your healers' mana resources.
Meanwhile, your other melee DPS avoids the flame gobs that Maggy spits, stands behind him or to his sides, and whacks at him. A single greater fire resistance potion per meleer will help a lot. Also, if your melee classes have fire resist gear, they should put it on for this fight.
Gehennas
The Gehennas fight is superficially similar to the Lucifron fight:
He has two guards, whom he must be separated from.
The guards die first, one at a time, then the main raid turns its attention to wiping out the boss.
However, the details differ.
Gehennas has two notable abilities: a fire AoE attack (Rain of Fire, which you must run from), and a curse that reduces the effect of all healing by 50%. The curse, obviously, must be removed immediately from anybody you want to keep alive. The AoE fire can be easily avoided by paying attention & moving if it's hitting you.
The pull goes a lot like the Lucifron pull: main tank holds Gehennas in place, the 2 assistant tanks pull the guards back to the main raid. The guards do a short-range AoE stun that can complicate the pull, so use ranged annoyances to move them most of the distance. The DPS groups focus fire on one guard, then the other, then move on to Gehennas. (The guards are, if anything, easier than Lucifron's guards.) Smack him until he falls.
Move away from the rain of fire.
If you're cursed and injured, run back to the triage area.
Garr
Garr is the most technical of the fights you've seen so far. If you've got a balanced group, with five warlocks, you're happy. If you're short on warlocks you'll work a bit harder.
Garr has 8 minions. You can't kill them all, because he goes into a major snitfit if they're all dead. In fact, he's boosted every time one dies. You can't tank them in a standard way, because he blows them up periodically. So you want to banish them, and keep them fairly close to Garr. In outline: banish what you can, kill what you can't, kill Garr, kill the remaining minions.
There are, of course, complications.
Garr has a nasty, nasty AoE movement slow. He also periodically eats buffs. You will lose all your buffs in this fight. Don't worry about it. You can rebuff afterward.
The minions explode when they die, doing AoE damage to everybody near them, and blowing them into the air. Don't be near them when they die.
Take them to 10% then finish them off with ranged damage.
This fight is made or broken on the pull. Get the pull right, and you'll be fine. We assign hunter/warlock pairs to minions, then assign a warrior to each of the remaining minions.
The groups spread out around Garr. The hunters pull their targets toward their warlock buddies. The warlocks pop on Curse of Shadows then banish their minion. Warlocks will spend the entire fight watching their banished minion and keeping it down. Sending their blueberries in to tank the banished mob can help them avoid aggro death on un-banish.
The warriors pull their assignments back away from Garr.
The main tank runs in to Garr to do his or her usual thing. The main raid then moves from minion to minion, killing them until only the banished ones are left. Then they move in and pile on Garr, who is pretty much a wuss with a lot of hitpoints. After Garr dies, take down the remaining minions one at a time.
Baron Geddon
There are a few things to know about Geddon:
Fight him in Garr's room, where you have space to move around.
He casts Ignite Mana, which manaburns your casters. Dispell it from them; ignore it on rogues and warriors.
He periodically stops, stands still, and sends out Inferno pulses. These are waves of AoE fire damage, each more than the last, winding up at 2000 a pulse. Run away! Run away! Even with high Fire Resist reducing the damage, you can't live through much of that.
He periodically casts Living Bomb on a player, who will explode in a few seconds. The player often lives through it, while taking out everybody around him. Don't kill your buddies!
The key to this fight is not killing yourselves with the Living Bomb. You must notice when you have the bomb and you must get away to a clear area to explode.
Have a hunter pull him back to Garr's room. Wear your Fire Resist gear; drink a fire protection potion. Have the raid spread out around Garr’s room, leaving lots of room around the right of the room for Bombs to run to (You will see the open space being made).
When the tank has aggro, dps gets busy. Everybody runs away during pulses. Everybody stays alert for Living Bomb and moves straight AWAY from the raid when they get it.
Melee should just stand well back and have a little dance while the MT does his thing. When he is down to about 10% all melee can suicide rush him and do as much damage as possible while trying to survive the inferno flames. (warrior should feel free to neck a rage potion and then hopefully survive till they have 100 rage and then execute him – You WILL die doing this)
Shazzrah
Again pull to Garr's room. Arrange yourself more or less the same way you did for Geddon, and stay spread out through the fight. Load your main tank up with arcane resistance if you can.
Shazzrah is very resistant to arcane magic.
It'll cast a self-buff that reduces the magic damage it takes. Dispell this.
It'll cast an AoE curse that increases magic damage taken. Dispell this as you can, but especially from the main tank.
It'll periodically do some Arcane Explosions. Clumped-up cursed players will die quickly, so stay spread out.
It has an AoE counterspell. Stay spread out.
It blinks periodically, reducing aggro and switching to a new target.
The blink makes the fight interesting. When Shazzrah blinks, the player with aggro must run back to the main tank. Everybody else must cease shooting, casting, healing, bandaging, or doing anything that generates aggro. If people are not paying attention to aggro,
Melee should repeat the tactics they did with Geddon and just stand around doing nothing until the last moment and rush in a give him a beating.
Sulfuron Harbinger
Return to Geddon & Shazzrah's room, and clear packs as necessary to head up the ramp. You'll start to get better at it with practice, though you might still lose a couple of players every fight. At the top of the ramp, stop to wave hello to Golemagg, who is very very tall. Then ignore him for now and continue down to Sulfuron. Clear his room entirely before facing him.
Sulfuron doesn't really do much of anything notable; he has a mildly damaging cleave. His four priest minions, however, do. They heal each other, and they cast a nasty, nasty Shadow Word: Pain. Keep it dispelled.
The basic outline of the fight: The main tank occupies Sulfuron while his minions are killed one at a time. Then the raid kills Sulfuron fairly easily.
Have the DPS gather facing the right end of Sulfy's platform. Assign each of the warrior/hunter pairs a minion, going from right to left. Pick an order for the minions to die. (Doesn't matter what order, but you might go in order from weakest to strongest for your off-tanks.) The main tank group heads in and tanks Sulfuron more or less where he stands.
The first hunter/warrior pair pulls their minion over to the DPS area to die. The others pull theirs out of range, to the left. One by one, the off-tanks take their minions over to the DPS group to die. (They will die quickly.) Then everybody piles on Sulfuron.
Enjoy the loot.
Golemagg the Incinerator
Golemagg is a very boring-looking giant. He's huge, yeah, but he looks exactly like all the other red giants you've been slaughtering for hour upon hour in the Core. Snore.
He does have a pair of puppies, however, who liven up the pit he waits in. I'm not sure what he's doing there in that pit. Waiting for you to farm him, it seems. So let's get to farming him!
The first thing to know is that you can't kill the dogs, so don't try. You will instead off-tank them through the whole fight while all of your DPS is concentrated on Golemagg.
The second thing to know is that Golemagg has a promixity buff for the dogs. So you'll be tanking them away from him. You can either pull them forward up the slope to you, or pull him forward and push them back to the wall. Set up two self-sufficient off-tanking groups: warrior, priest/druid, paladin/shaman, maybe a warlock for the imp buff. Keep those off-tanks up!
That leaves Golemagg. It's a long fight, so be prepared to endure. You might want a healing rotation. Have some mana potions at the ready. He has two abilities worth mentioning: a fireball he shoots at a randomly-chosen secondary target, and a DoT/armor debuff that stacks. The DoT effect is only applied to people who are attacking him. Your meleers should consider pulling back and waiting out the timer when it stacks to 3 (150 damage per tick). Your main tank can also do that (have other people hold off when he or she does to avoid aggro problems).
Fire resist gear will help. Also, fire protection potions will absorb quite a bit of DoT damage.
At 10% the fight changes pace. Golemagg casts an odd aggro buff on the dogs that boosts the aggro of everybody except the previous #1 target for the dog. Your off-tanks need to be ready for this. At 10%, pull all your healers in and let rip with the DPS.