Group Makeup
Our group makeup was the following:
Prot Paladin
Feral Druid (I believe in a mix of dps and tank gear)
Holy Paladin
Resto Druid
Elemental Shaman
Demo Warlock
Frostfire Mage
Rogue
Unholy DK
Shadow Priest
Basically you need 2 tanks and 2 healers with at least one hybrid healer (moonkin/ele shaman/shadow priest), with at least 4 ranged dps. I can not stress enough the importance of ranged dps on phase 1 yogg, we went from 3 to 4 and proceded to down him within 2 attempts. The second tank tank is needed in both phase 1 and phase 3, so having a dk tank or a feral helps alot b/c they can dps in phase 2.
Watchers
They are a very important part of the fight so I'm going to go over what each does, and as you read this realize that each level of the hard mode removes one of them. Just the thought of this makes me dread the hard mode of yogg.
Freya: Freya gives the entire raid this buff http://www.wowhead.com/?spell=62670, which increases all damage done by 10% and all healing received by 20%. Also Freya puts giant green pillars of light in the corners of the room, by standing in these beams you gain 20 sanity a second but do reduced damage.
Hodir: Hodir gives the entire raid http://www.wowhead.com/?spell=62650, which increases all damage done by 10% and reduces all damage taken by 20%. Also Hodir will encase a member of the raid in an ice block to save them from a blow that would have killed them. After he does this he must "rest" for ~30 seconds before he can save them again.
Everyone in the raid needs to make the following macro and use it when you get encased to break yourself free or your stuck in the ice block for the entire duration. (On a side note if you have the "Fail mod" it counts these saves as missing the Hodir flash freeze ability)
/cancelaura Flash Freeze
Thorim: Thorim grants the entire raid http://www.wowhead.com/?spell=62702, which increases damage by 10% and health by 20%. Also during phase 3 Thorim will throw his hammer at the adds that spawn. This is important b/c when these adds get to 1% they go immune to all damage and the only way to kill them is to have Thorim kill them.
Mimron: Mimiron gives the entire raid this http://www.wowhead.com/?spell=62671, which increases damage by 10% and increases run speed by 20%. The second effect from Mimiron is a curse-of-tongues effect on the Corruptor Tentacles, reducing their cast speed by about 300%. The effect seems to occasionally drop out for a second here and there, allowing some casts to occur full speed (most likely a bug)*.
Sanity
The key to this fight is managing your sanity. As the fight starts you have 100 sanity, and as the fight starts yogg will start using different abilities which will reduce your ammount of sanity. You can get your sanity back by standing in the green pillars of light in the corners of the room.
Phase 1
As you look into the room notice a few things. First notice in the middle of the room is the woman that's been annoying you with her constant screaming, Sara. She is friendly and can not be attacked. The second thing to look at are the swirling clouds around her. Third are the pillars of green light around the room.
First I'm going to go over the clouds. If you touch any of the clouds they make the clouds form a swirling giant green orb, after ~10 seconds a guardian of Yogg-Saron spawns. These clouds are on 5 concentric circles each further out from sara in the middle. There is one cloud on each cirlce and they will move either clockwise or counterclockwise.
Diagram of Gas Clouds

The adds will spawn randomly form one of the green gas clouds that are rotating around the center. The mob needs to be dps'd down at some point (we used a spot in the 3-5 rings so melee wouldn't have to dodge the explosions) and then brought in. Basically its a kind of frogger for the tank to get to the middle or another good way to think of how this works is the lockpicking mini-game from the pc version of Mass Effect.
Second is the adds that spawn, they are called Guardians of Yogg-Saron. They form from the green clouds that cirlce Sara, they start slow at first and will speed up as the fight goes on. They are pretty basic and have one abilbity, which is dark volley. Dark volley is a casted spell (that can be interrupted) that casues a 25% mortal strike debuff on everyone it hits, this is a large area too if I had to guess I would say 30 yards. Also when they die they blow up for ~16-17k damage.
Finally you need to be aware of a debuff that sara will cast on random party members. It's called Sara's Fervor (http://www.wowhead.com/?spell=63138) and will increase damage taken by 100% so its important that you try not to tank when you have this. It will eventually become unavoidable near the end of p1 so just save a shield wall for when you need to blow up your guardian.
The point of this phase is to kill Sara by blowing up Guradians on top of her. Two tanks seems like a waste at the start of this phase but is very important near the end when they start spawning faster than you can kill them. There are two very important rules;
1) Never touch a cloud, you will get overwhelmed or will be forced to blow a lust
2) Never kill a Guardian until it gets to her, because missing an early guardian forces you to kill a late one which will leave give you at least 1 if not 2 guardians to deal with at the end of the phase 1.
We found it best for melee to stay on the outside of the pool where Sara is standing, the point of this is melee can't be in the middle when the guardians explode. Having your melee move in and out of the center is just asking for either dps to clip a cloud or to have to sit on their hands as they make there way through the clouds.
While ranged focuses on blowing up the add that is in the center, and moves back to the next guardian during times where there is no guardian in the center. It is very important that you interrupt the Dark volley's because they will make this phase incredibly hard on your healers near the end.
The mantra for tanking the guardians is "It is better to go slow and take the long way around than to chance hitting a cloud". I can't stress this enough, the spawn range seems to be slightly bigger than the cloud graphic so be advised, also don't try to cut b/w two clouds going opposite directions just wait on the inner one to be clear before you go.
During this phase Sara will also mind control people, this is a magic buff that can be removed and needs to be removed. We have had wipes b/c the holy paladin wasn't dispelled fast enough and he ended up being dispelled int he middle of two clouds.
Sara has 160K life, and requires 9 guardians to die on top of her (it may be 8 I didn't count b/c of how hectic it gets near the end), after she "dies" she reveals her true form as the god of death.
Now the fun starts.

