"beat the system" tip 2: how to make the preassigned seating paradox work for you.
 

People with preassigned seats will probably have asked for the best seat.

If you are not satisfied with your seat-assignement ask the staff to be waitlisted for a better seat before the standbys

If the flight is overbooked: the preassigned "good" seats from the no-shows will go to the standbys;

If the flight is underbooked, the no-show-seats will not be assigned, pick-them after the door closes.

(from the airline passengers guerilla handbook).