The tank should start the fight and pull Illhoof next to the center of the room where the Sacrificed target will be placed. He is fairly easy to tank and not much else needs to be done. Though possible to solo tank, a second tank can be used to tank Kil'rek and make sure its kept off healers and AoE casters.
Once Illhoof is pulled he will spawn 2 portals at the back of the room causing Imps to continuously be summoned. These should be AoE'd down since they will gather around Illhoof to cast on the healers. Warlocks Seed of Corruption is huge here.
Chains MUST be taken care of ASAP and DPS should have a macro to quickly target them.
/tar Demon Chains
Left unkilled, it will damage the raider and heal Illhoof which can be quite detrimental to the raid. Hunters should use Snake Traps because they can be targeted for sacrifice.
Kil'rek should be focused down to help prevent unneeded damage on the range AoE and healers. Doing this also keeps the Broken Pact debuff up on Illhoof.
Keep Illhoof and Kil'rek next to sacrifice circle
OT should dps while Kil'rek is dead.
Chains are top priority
Casters AoE to kill summoned imps
Sacrificed victims must be healed asap
OT will take damage when Kil'rek is alive