Here are The Traveling Professor's tips for getting the best coach class seats on the plane:

Check the Seating Chart:  Most airlines allow travelers to check the seating chart online.  If it looks like the flight is empty, don't even worry about strategizing a way to get a better seat.  Travelers will probably be happy with whatever they get.  However, if the flight looks to be full or close to full, it might be a good idea to look at some of the tips outlined below.

Hate the Middle Seat?  Buy It:  Most travelers prefer window or aisle seats which can be selected either for free or for a fee.  But what if you want to leave that middle seat empty to give room to stretch out and enjoy the flight?  Most airlines permit the traveler to buy the middle seat or better yet, buy it with frequent flyer miles.  That guarantees the seat next to you will be empty for the entire flight.  And, if purchasing the middle seat to remain empty, that seat may be exempt from some taxes.  Travelers may need to call the airline directly to purchase the middle seat if no one will be occupying it.  Of course there may be an extra expense with this strategy, but it is probably less expensive to buy the middle seat than to purchase a single business or first class seat.

Book the Aisle and Window Seat and Leave the Middle Seat Empty:  This can be a gamble, especially if the flight is full.  When The Professor flies with his companion, this is a common strategy.  Since the middle seat is the least desirable seat, it is usually one of the last to be selected by another passenger.  If the travelers are lucky, no one will be assigned that seat.  And if someone does select the seat, I will offer the person who has selected the middle seat to move to the aisle or window which they always accept.  I can then sit next to my travel companion.

Book Early:  Some seats are assigned on a first-come, first-served basis.  Seat selection is obviously best when booking before others.

Book the Exit Row:  Exit row seats offer more space.  However, the arm rests are usually stationary and there may be a fee or restrictions for booking the exit row.  Also, there may not be any under seat storage in the exit row.

Avoid the Bulkhead Seat:  Although bulkhead seats can offer extra room, there is no under seat storage.  The arm rests usually are stationary.

Avoid the Back of the Plane:  The traveler may find it will take 15 minutes or so to disembark from the plane.

Enroll in an Elite Status Program:  By enrolling in an frequent flyer program and gaining elite status, roomier and preferred seat locations are often offered to travelers at a reduced fee or with no fee at all.

Ask the Agent:  When checking in, courteously and politely ask the agent for a better seat.  Sometimes this works, sometimes it doesn't.  But it doesn't hurt to try.