What I notice as a new player (used to tanking in other MMO's), Due to not knowing the layout and how hard certain trash hits, I tend to use cooldowns to much. Which sometimes bites me in the ass.

When there's room to pull 2 packs, ofcourse I'll use some cooldown until the group is thinned out enough to survive easy and have something up for the next pull. Some more experience will make sure this will go smoother.

I don't know why tanks wouldn't use their cooldowns, they're made to be used.