Also, know where your flight is coming from and if it is continuing (and how many through passengers are already on the plane). Nothing like having an A boarding pass and being towards the front of the line, only to get on and see that between all the through passengers and pre-boarders, you are heading to the back of the plane or even a middle seat.

Has not happened to me since moving to LA, but did happen a few times out of BWI (previously mentioned flights to Orlando a good example).