Know the rules (and restrictions). Before buying tickets, check with the carrier you plan on using to find out what its policies are for flying with babies. You'll want to know in advance if there is a charge for the babies and if they can sit on laps, along with the 411 on getting formula or breast milk through security. Figure out if the twins will need passports or what type of ID you should bring to the airport the day of the flight.
Be flexible with your parenting rules. You may want to loosen your own restrictions on the twins when you're up in the air. One treat per day may make sense at home, but when you're flying you'll be happy for that extra bag of Goldfish.
Choose your flight times wisely. The first flight of the day is usually least likely to experience delays. Although it's hard to get everyone out the door for an early-morning flight, the lower chance of delays makes it worthwhile. If your babies are using car seats, try to schedule the flight during naptime. If they're sitting on your lap, try to fly when they're alert.
Decide ahead of time where your babies will sit. On most airlines, a baby is allowed to travel for free on your lap until age 2. You can fly with your baby in an FAA-approved car seat, but that means you must purchase a seat. Remember, if you choose the lap option, the FAA does not allow two parents with lap babies in the same row, so book your seat on the aisle and your partner's seat in the other aisle seat of the same row.
Leave extra time. You've probably figured out by now that doing anything with twins takes a little more time than it used to, but because flying is already particularly stressful (especially if it's your first time with the bambinos), having a little extra time makes sense.
Bring a change of clothes. Extra clothes for both babies is a must on the flight, but don't forget to pack a change for yourself and your partner (just in case that little accident ends up on you!). While you're at it, stash a few extra diapers and an extra bag of wipes in the diaper bag.
Scope out the seats. Most airlines allow you to go online and check for open seats. If your flight isn't full, there's a chance you could be allowed to bring your car seat on board (even though you haven't purchased an extra seat). Keep in mind that if you are forced to gate-check your car seat, it could get damaged, which may compromise its safety.
Have help. Flying solo with twins can be done (some airlines will give you assistance to the gate or give you a gate pass for another adult). Services such as Nanny in the Clouds can be invaluable when trying to entertain two tiny tots.