I started flying with my bike back in 1989. Back then it was easy—walk into the airport, get a free box, take off the pedals and handlebars, pack your gear in with it, and off you go. It’s been a long time since 1989. I’ve now flown with a bicycle, hmm, 27 times? Every trip since has been just a little bit harder. I’ve learned a lot of lessons among the way, and thought I’d pass a few of them along.
In no particular order:
-Bring enough tape to repack the box. Either the airline will want you to open it, or you’ll want something in or out of it.
-Have a printout from the airline website on the shipping requirements. Expect that they won’t care if their opinion differs.
-Know the airline requirements and the size of your box.
-Bring enough money to pay to ship the bike, even if you have the printout from their website with you (because you can’t win that fight at the register, you can only win it later with the airline) that says you won’t have to.
-Know all the requirements for ALL the airlines you might be flying on (if you have a transfer to another airline). It’s supposed to be by the starting airline, but again, the people at the counter won’t always get that right.
-Have something you can open the box with when they insist you open it, even if you’re not supposed to have something sharp. And tape to repack it.
-Have a backup plan for when they decide there’s something in the box you can’t take with you.
-Pack the peanut butter in with your luggage, not your carry-on. It could explode in your carry-on apparently, but won’t in checked luggage.
-Disconnect the rear derailleur; it’s a lot more resistant to getting banged up if it’s loose.
-Use the toolkit you’ll travel with to disassemble the bicycle. That way you know you have the tools to put it back together.
-Bring even more tape. No, really.
-If using a cardboard box, solidly reinforce the handles on the side of the box with tape and cardboard. The box comes through a LOT better that way. If the luggage handlers have the handles on the box tear out, they just throw it everywhere after that (at least that’s what it will look like). You can use your extra tape.
-If in a cardboard box, protect the forks by placing a rod in the middle where the axle would be, with washers and nuts to prevent the forks from getting cracked if someone squashes your box. Something like this (tho in this case I had my front racks to also deal with): 
-Loosen your pedals the day before, so if you can’t get them off, you have time to appeal to external resources, not while you’re frantically preparing for your flight.
-If your pedals don’t mark Left and Right, mark the Right one.
-When loosening your pedals, make sure the chain is on the largest front chain ring. If the wrench slips slip it will hurt, but it won’t hurt nearly as badly.
-Disassemble your bike with only the toolkit you’re taking with you.That way you know you have all the tools to put it back together.
-Deflate your tires. The airlines care. They might make you open your box for this.
-If you have layovers, plan your flight so that layovers are 3-4 hours, not 30 minutes. Long enough to be sure your bike gets there, short enough it (hopefully) won’t get lost. Long enough so that minor flight changes won’t cause your bicycle to miss the flight. That also provides enough time for the bike to be inspected when Customs decides it’s important. In the rare case your bike misses the plane for the connecting flight, more time provides the airline the opportunity to get it on another plane in a reasonable time frame.
-If your bike misses an international flight, it will probably arrive on the same flight the next day.
-Use electric tape to mark the positions of your seat and handlebars.
-tie-wrap everything in the bicycle box in place so it’s not loose. They’ll likely open the box along the way, and not care nearly as much as you to seal the box well.
-Luggage handlers can also tear a hole in your box.
-If you plan to pack your bicycle at the airport, give yourself far more time that you think you need. Something won’t go well.
-Pack your tools in with the (checked) bicycle. You might be tempted to hijack a plan with a hex key otherwise.
-In the days before your flight, identify bicycle shops in the departure and arrival cities—just in case.
-Try to make sure the bicycle is clean, especially the wheels. Mud on the wheels will raise eyebrows from Customs officers in some countries (NZ comes immediately to mind).
-Most airports have a special oversize carousal meant for golf bags, bicycle boxes, surf boards…etc..separated from the normal luggage. And in some airports that have more than one, and won’t know which one is the one your bike should appear on. Or will tell you the wrong one.
That’s at least a good start. What other suggestions do people have?