Situational Awareness : that maybe just because you are not used to the job yet, or because some people will have some affinity with such gameplay but not with another no matter what they do. I say that because MCH is by far the job where i nearly dont need to look at all at my icons, buffs or the heat jauge, and have plenty of time to look at the boss and mechanics themselves. While if i switch to my BLM (only lvl 30) i will have the same problem as you have with your MCH, looking too much at my mana bar to see when it become too much empty and checking if transpose is up yet. Or how i have a hard time with my 70 RDM in raids, despite the fact that i do 4k dps on training dummies, when i enter savage i drop down to under 3k, because instead of dpsing like mad while looking at what the boss is doing, i check way too much my buffs and jauge, or my team life bars to know when i am must correct a healer screwing up things.

Mid-Fight Wildfires : usually if i begin to get some skills being misaligned, it is because i have screwed up launching them correctly some time ago, for example a key that didn't work or the boss suddenly disappearing while i was in the middle of my wildfire combo.

AOE Situations : if i know that i will be aoeing a lot (dungeons, Uznair's canals) instead of single targeting (raids), i now switch to my RDM XD