Grounding Totem is the main priority, and it helps to throw them down first since this lets the cooldown come up faster. If a fear is imminent and I have no totems down I will simply drop a Tremor on my main and then go for the cast sequence there after.
The only other situation is that you get blindsided and you didn't see it from the get go which results in trinketing on the main and hitting tremor which snaps everyone out of it.