If your are the Green Ooze target:
If you are isolated and nobody is coming to you, you can handle it alone by Ice Blocking before, but take care it don't really absorb damage, it just prevents you from taking it. As you know the damage caused by the Green Ooze hit is shared between the people in its melee area. If you Ice block this damage, it will be redistributed between your mates. So if you are barely enough people to survive the explosion, the fact you Ice Block will lead to the death of you mates.
If you are a bit far away from the pack, you can blink in their direction to join them, even if the attack normally locks you in your place.
If you are well placed and your mates are doing good, do nothing to move or avoid damages, you will certainly disturb them !
If you are the Red Ooze Target:
Remember you have Blink and Nitro boots to go away.
Try to move the Ooze around the boss melee hitbox, this way your Mdps will optimize their own Dps.
If a Malleable Goo: comes right on you:
If you see it until the launch wait for a GCD and moove out of the damaging area, it's enough even if you are the target (remember you need to move 5 yards away not a lot more, because the damaging area is 10)
If you are not confident blink away, you can't be hit by a goo as a mage, it's a shame if you are.
If however for some reason you did get hit by malleable goo, you can Ice Block it instantly to remove the debuff.
General Advice:
Stay on a 6 yards range from you mates all the time, in order to properly see if you are the Goo target and only move on the Goo the boss launch especially on you.
Try to find a location where you are at range to always hit both oozes and the boss.
If you have good healer, wait for a GCD before going out of puddles they can handle it. (only for Fire Mages)
Remember as a fire mage you have an high mobility so you can help your mates by carrying the plague from a group of Rdps to another without loosing any dps. (Only for Fire Mages)
For the rest is usual heroic tactic.