This fight may seem complicated due to the randomness of it. However, with a bit of coordination and communication, it's very controllable and doable.
To begin, my raid arranged itself in a circle around the middle, using the points of the star as markers. The areas directly in front of the instance door and directly in front of the boss entrance were left open. After that, two ranged each sat on points of a star to minimize spreading damage, like the chain lightning ability or the fire drops. Every person who became affected by Legion Flame then had an area to run straight backwards to drop their fire (Legion Flame does a DoT and causes you to drop patches of fire where you are standing that do heavy damage once every second for six seconds). We kept the spread of healers even, and monitored people for Incinerate Flesh.
Incinerate Flesh is a little bit of a weird mechanic in that your target will not noticeably be taking damage. The debuff absorbs 60k healing and decreases attack speed by 50%, and persists either until 60k healing is absorbed or fifteen seconds pass. If you don't heal enough, then the person will gain a raid-wide DoT for 3K+ every second for five seconds. And while this may not seem too bad, there is a lot of incidental damage going out, and this is so completely avoidable as to have no excuse for the person not to gain heals.
During the encounter, Jaraxxus will summon an infernal volcano. You should have one or two OT's responsible for managing these brutes. They have an AoE just for standing near them, so ranged should nuke them down and you should get out of their way. Try to recover quickly from any charges they get off and heal any people affected.
Jaraxxus will also summon Mistresses of Pain during the encounter. When he opens the Nether Portal, he'll gain Nether Power, a 20-stack buff that needs to be dispelled and purged and spell-stolen as quickly as possible, and at this time you need to watch the tank as he'll be taking more damage. The Mistresses of Pain need to be controlled as well as possible and kept away from melee. Ranged should power her down, as they can keep clear of her armor-ignoring attacks. The reason she is so hard to control, however, is the Spinning Pain Spike. This causes her to leap upon a player (kind of like the snobolds in the first part of the Beasts) and, well, hurt them. These people need to be called out quickly, as she'll pick them up and slam them into the ground for a percentage of their maximum health.
It certainly sounds like a chaotic fight, and it certainly can be. However, with a little bit of coordination, the chaotic, random side of the encounter is diminished greatly, and a win is much easier to obtain.