Right as I'm walking on, I give the piece of aluminum fuselage immediately to the right of the entry door a couple quick pats. Purely for good luck. (If you ever see anyone doing this while boarding a NW flight, it's me. Say hello.)
When I get to my seat, I throw my backpack under the seat in front of me, put my water bottle and a magazine in the seat pocket, and start people-watchin' until the door's closed.