I have two kinds of experience here. One is transatlantic (Chicago to Madrid en route to Rome/Athens), and the other is domestic, but long-haul (Chicago to Anchorage via Phoenix).
Internationally, Iberian Airlines was okay. Not super great, but not terrible. I believe we were in an Airbus 340, and the seats were…well, they could hold me, and I was pretty big at the time (and “pretty big” is an understatement). The staff were reasonably polite and courteous. I was surprised that we got both dinner and breakfast.
If you’re awake, as I am, make sure you walk about some. You’ll feel less crappy, reduce the chance of leg blood clots, and make it out of there less stiff than you otherwise would. Bring a decongestant if you’re often stuffed up, and take it before you take off. Unless it makes you jittery and wired, in which case, find one that doesn’t and take that instead. Bonus points if it includes a painkiller. Double bonus points if it knocks you out. This advice comes from flying domestically on the tail end of a cold. I was in agony due to the pressure changes.
Make sure you have your passport somewhere you can access it without having to get up into the bin or otherwise contort yourself. You’ll need information from it to fill out the customs form, and it’s just awkward to have to go through the overhead compartment mid-flight.
If you can, one bag it. This greatly reduces the chances of complication if one leg of your flight is delayed; I especially recommend using something you can carry on your back or shoulder, as I wouldn’t want to muscle a rolling bag through rush hour on public transit (Rome was like freaking sardines, even on the train from the airport). Also, it gives you more flexibility; twice now I’ve taken earlier flights in order to shorten my layover, and I wouldn’t have been able to if I’d had checked baggage.
Expect the plane to be full. You wouldn’t expect, say, a plane to Anchorage in the middle of January to be full, but it was. Plan accordingly. As slaphead said upthread, lesspectations are key.
