Move fast and keep looking: When booking a flight, immediately choose the best seat you can, then keep looking to see whether you can improve your position, even after you get to the airport on the day of departure. If you don't mind paying, departure day is the time airlines often drop prices on seats that no one's shown much interest in and they might be willing to dicker, especially on international routes. Check at the kiosk, check in the airline lounge, check your smartphone's app and look for last-minute seat deals.
If you're really obsessive, check out one of the many "seat review" sites; there are plenty of them.
The two-for-one deal: If you're what airlines refer to as a "customer of size," you already know you're supposed to be proactive and purchase two seats. Southwest has famously thrown larger fliers off planes -- those that didn't adhere to the carrier's two-seat policy, in any event, but many still hesitate to buy two seats. Who wants to pay double? But here's the good news: If the flight is not oversold, Southwest refunds the money for the second seat. So you get the extra space for nothing. There are no guarantees but if it happens, it's a sizeable deal by any standard.
Choose seats in the rear of the plane: The rear of the plane is usually the least popular part of an aircraft (its proximity to the restrooms might have something to do with that), but it's usually where you'll find open windows and aisles. At the very least, aisles offer some "stretch-out" space for longer legs and as long as you remember to keep your feet out of the way when the drink cart comes through, you'll be fine.
Fly mid-week: As mentioned, there are few empty middle seats these days, but you'll probably find more on "slow" travel days like Tuesday, Wednesday or Saturday.
Just pay the fee, you might be surprised: American Airlines' "preferred" seating option can be as low as $4 and when you figure their fruit and cheese plate goes for $8.29, the seat is a deal. Prices for premium seats vary from airline to airline, but, generally, the longer the trip, the higher the price. Southwest uses a slightly different method: Pay 10 bucks for their cut-in-line boarding queue and you pretty much have a choice of seats, including exit rows and bulkheads.
Can't find a decent perch and the supply of fee-seats is exhausted? Chalk it up to that annoying shrinking ray, but next time choose your seat the moment you book your tickets. Everyone's doing the same thing, but he who strikes first will be the most comfortable.
The opinions expressed by Rick Seaney are his alone and not those of ABC News.