What I need to focus on varies on any given day. I have literally written post-it notes and stuck them to the edge of my monitor saying "Small hands play small pots" or "Read the notes you make on villains"
The fundamental things I think about pre-flop are:
Button, button... Who's got the button? (Does anyone here get the reference?)
Hello. Yes, this is Hero. Who's calling, please?
How deep is everyone? I'm not trying to put Descartes before the horse (or donkey, as may be).