I do prepare. I won't run a new raid or dungeon unless I've at least watched enough training videos, so I know what to expect. I recently ran Eden 4 for blades, and made sure I watched the vid for that. since I hadn't run it for a month. (Still died 3 times

Recently, my FC pulled me along for a copied factory run on the first day, and it was a disaster. I think I died about 20 times in that one.. I'll never run another instance blind again.