Give yourself plenty of time. Everything takes longer with a baby in tow, and traveling with your little one offers plenty of last-minute surprises (a poopy diaper, spit-up all over you and baby, etc.), so be sure you plan ahead and leave with plenty of time for the airport.
Pack light. You don't need an overstuffed diaper bag--it's one more heavy thing to carry through the airport. Unless you're going on an especially long flight, bring one carry-on for the both of you, and put in only Baby's necessities: diapers, wipes, a change of clothes (in case of an accident), a Binky, bibs/burp cloths, bottles, and a few toys.
Wear your baby. It's easier to maneuver through the airport with Baby in a carrier or a sling than to in a stroller. The stroller can be a pain to open and close at security check-ins, and you'll most likely need to check it with your luggage anyway.
Dress comfortably. Both you and Baby should be wearing clothes that will help you relax during the flight. Planes can get pretty chilly, so be sure to bring along an extra sweater or blanket for the baby.
Feed during take-off and landing. It will help pop your baby's ears during the elevation changes. But if he's sleeping during these times, you don't need to wake him up.
Board first and deplane last. You'll have a better chance of getting assistance from the cabin crew.
Ask for help. The airline attendants should be more than happy to help you, from heating up bottles to setting up the restroom changing table. After all, they don't want a cranky baby on the flight any more than you do, so it makes sense that they'll assist you when they can.
Don't worry. Even if your baby has a meltdown on the plane, don't freak out. Chances are that there are quite a few parents on board who have been through the same scenario. Crack a joke, give them a smile, and realize that this flight won't last forever.