Where will the boss be?
Lord Jaxx will be picked up in the very center of the room by your MT. Your OT will be picking up other adds around the room though, in the approx. location that they spawn.
Where should I stand?
All ranged should organize themselves into groups of 2 or 3 around the room in a large circle, making sure all raid members have access to heals. Due to this spreading out, some healers may be out of range of raid members during the encounter, so when you have been assigned a group and a spot around the circle, take special note of who is in your group, and the groups on either side of you. It is going to be your responsibility to keep them alive.
What should I look out for?
Fel Lightning - The reason why you will all be split into little groups is due to this. Jaxx will target a random ranged member and hit them with this lightning, which will then chain to anyone within 10 yards. Use Rej's, LB's or your WG to mop up the groups that take this damage and, throughout the encounter, as you dodge adds and flames, be sure to always move back to your original position to avoid a mass chain lightning effect.
Legion Flame - A debuff that will target random ranged or melee targets. It will tick for large amounts of damage and leave a aoe effect on the ground, causing addition pain for anyone willing to sticka round in one. If someone has the debuff they will need some good strong heals. A regrowth and a Rej or LB stacks is a good starter, and keep an eye on them incase they need a Nourish or two. If YOU get the debuff you need to turn around and run towards the wall behind you, leaving the trail of doom safe away from your friends. As you are running be sure to give yourself some LB's and a Rej, as you are going to run OOR of healers around you.
Incinerate Flesh - A ticking timebomb that does raidwide damage to a random target. The way to get rid of it is to simply heal the debuff off. If a raid member gets this you need to get heals on them right away. It will be all overhealing but do not stop until the buff wears off. 10 man raids will need to heal it's targets Approx. 30k to get it off, and 60k in 25 man raids. Nourish is your friend here as it will give you the large fast heals you need, no time for HoT's. If YOU get this debuff, It is probably a good idea to call it out, and make sure you are in range of as many other healers as possible, so they can help you get rid of it.
Nether Portal - These portals will appear during the fight and will spawn a Mistress of Pain. She will target a random player every so often, tossing them in the air and inflicting damage equal to 1/2 their max HP. Be ready to top up her victims with a Nourish or Rej+SM combo.
Fel Volcano - These get summoned by Lord Jaxx and do AOE effect damage to anyone standing within 10 yards. Be sure to dodge these if one spawns near you, And use your WG's for any groups that get hit. These volcanos will also spawn fel inferno's, dealing more damage to your OT.
Any Healing assignments?
In a 25 man raid we will assign 2 healers on each tank and the remaining 1 or 2 on raid healing. My guild do not assign Legion Flame or Incinerate Flesh healers as range can sometimes be an issue with this fight. If you are in range of these targets, do your bit and help out.
Goodluck and have fun!
Wow Slang Dictionary
WG - Wild Growth
Rej - Rejevenate
SM - Swiftmend
LB - Lifebloom
MT - Main tank
OT - Off tank
HoT - Heal/s over Time
OOR - Out Of Range
AOE - Area of Effect