Attumen the Huntsman (patch 2.4.2)

This is the first boss in Karazhan.

First Phase - The first phase of the fight is just Midnight the horse. Midnight does not do any AoE or anything special really so just heal the tank. Searing totem is recommended because once Midnight is at 95%, Attumen will spawn and runs into the middle of the raid group, and the searing totem will usually get picked up by Attumen so that gives a 2nd tank (usually the Main Tank) time to pick Attumen up.

Second Phase - Attumen does a nasty cleave so stay away from him. The only people that need heals are the two tanks, unless some other players stand in front of Attumen. When Attumen or Midnight's health is down to 25%, Attumen will mount Midnight. Aggro resets when they mount, but good tanks can easily pick that up.

Third Phase - Stand directly behind Midnight's butt to prevent charges. The charge does a lot of damage. I'm not 100% sure but I think the boss charges the person who is furthest away from the raid group, which is usually the hunter if you have a hunter in the group. Use bloodlust and searing/fire elemental totem to help speed up the fight. Again, the boss will cleave so please make sure you are behind him. Just keep the main tank and anyone who gets charged top off in heals (and anyone who gets cleaved =/). The end.

Critical Strike Rating for Resto Shamans (patch 2.4.3)

Many resto shamans do not see the importance of critical strike ratings for healing. Since this is a raid healing guide for resto shamans, I'm going to discuss about chain heals as chain healing is used 90% of the time in raids. There is a chance to crit on each jump of the chain heals which totals to a chance to have 3 crits in a row with ONE cast of chain healing. Also, assuming you have 3/3 talent points on Ancestral Healing (Increases your target's armor value by 25% for 15 sec after getting a critical effect from one of your healing spells.), I can't stress enough how important critical strike rating is. With higher chance to crit, you should be healing more than another resto shaman who has a little bit higher healing bonus but less chance to crit than you.

Even though spell crit is important, around 15% spell crit is all you really need (assuming you have 5/5 Tidal Mastery, you will have 15% spell crit on heals even though it shows 10% on your character stats). As your guild progresses into T6 contents, you need more focus on spell haste gems than crit gems.

Edit: As a resto shaman, you are usually designated to be a raid healer. Main tank healers are usually designated to paladins and priests. Most bosses deal non-physical damage to the raid, which makes Ancestral Healing useless to heal the casters and other healers. I am a raid healer in guild so my job is to top everyone off from AoE damage. Also, Ancestral Healing does not stack with Inspiration (priest's talent). I'm not telling you not to get Ancestral Healing because it is personal preference. The raid is not always perfect because main tank healers can die, and you would need to top up the main tank.