Look guys with all respect, PvP and PvE are very different from eachother. In PvP you react to your opponents and do what you think is best at that moment. PvE on the other hand you are managing very tight timers and making sure you don't miss ticks or uptimes on a ton more abilities. It's understandable when you suddenly have to manage milliseconds on multiple different things to suddenly have trouble with this thing that is quite normal and natural in PvE. In PvP your goal is killing someone, in PvE you are being compared to 24 other people on a list.
Gregz, it's not really your fault, most of the time in LFR you get inexperienced tanks who constantly move all the time for no reason at all. It's the tanks jobs to keep bosses stable at all times. The melee in my guild would go insane if we had to deal with LFR tanks.
This sadly. Side note, it's not exactly the most helpful having a monk tank as they want to pick up their orbs, which requires them to move around a little to do so.
Try to hang out with the pets (Hunter or Shaman) that always reposition to the back of the boss. That way you don't even to worry about where the tank is facing the boss, you'll know where the game considers the back to be. (If it's a Hunter pet and you see it jumping around a lot, that's Lynx Rush, don't try to follow. Although feel free to cast Killing Spree at the same time)
That said, watch your feet: most pets ignore the stuff on the ground.