If your flight is canceled, call the airline’s registration number immediately (have it previously programmed into your speed dial).
For a better seat
Check online the day before departure to see if new seats are available, or ask at the gate, airlines release more seats just before takeoff.
Playing the bumping game
If your itinerary is flexible, ask at the gate if the flight is overbooked. If it is, ask for the airlines initial offer and get on the volunteer list (the list does not commit you but gives you right of first refusal). If you do not like the offer, you can hold out to see if the airline will sweeten the deal. If offered a free ticket, ask if there any restrictions, such as an expiration or blackout dates, and make sure you get a confirmed seat on your next flight.