Call me nuts BUT,
My standard procedure when sitting in an airliner...
Look at the general exit distance, count the number of rows to the nearest exit on BOTH sides. Sit down, look for the lifevest, then strap myself in, look at the safety card to determine the type of lifevest (is it a tie-it-yourself, front centre clip or a side clip type) and the type of door and slide config, then make sure my hand can reach for the emergency oxygen thingy should they be deployed.
If possible, I look at the types of people sitting between me and the exit rows and alternatives. This will enable better anticipation of pax behaviour when evacuation.
At top of descent, the same procedure applies except the oxygen masks...
Other than that, some general notes... Airport config, general observation of water and mountains surrounding the airport.
People have called me nuts, but then again, I have a liferaft, a pair of lifevests, a pair of helmets, written contingency evacuation plans for local and citywide, have a 737 pilot on my speed dial for citywide emergency evacuation (where the jet is fueled up for a 2 hr flight every night and Carry an AirNav map out of the country in my work bag.
When losing situational awareness, pray Cumulus Granitus isn't nearby !