I thought I would make a short visual guide showing how ranged players should handle Fel Incineration.
I'm not going to go over what it is, or how it works (watch a video!). We're just going to dive right in.

Okay, so here's the first diagram - starting position for ranged and healers. Moving on..

Random people start getting targeted with Fel Incineration.
Run out of the group in a straight line towards the wall and back. You're simply making an "L".
Eventually Iskar goes up in the air, adds come out, and Phase 2 begins.

Everyone transitions to the middle. Notice in this diagram there are still fire lines on the ground from Phase 1.

Incineration again - those targeted should be kiting the fire to the side we just came from - in this case Green.
Once the adds are dead, and Iskar has shot his 2 lazers, we move to the opposite side.

Fires will probably still be burning on Green side and Middle (I forgot to draw them in)

From this point on, it's basically rinse and repeat - only switching sides.
Any tips or tricks?
No, not really. The important things to take from this guide are not to panic and start doing figure 8's around the group if targeted. People will get hit by fire, but it's up to them to be ready to adjust. That's also why it's important to make a clean line out of the group. The less adjusting we have to do, the better our DPS.
Also, find what works for you. For me, it's positioning. I stand further up from the ranged group, so if I do get targeted and make a terrible line, I'm still only causing 1-2 people to adjust.
Have questions about positioning or how to handle a specific mechanic in HFC? Shoot me a PM, or leave a comment and I will make a guide.