Never fly an American airline. While it's largely true that American stereotypes are exaggerated, I've never felt more intense hatred than being on a flight with middle class Americans with their neck pillows, flexible footwear they change into in the seatrow, the gigantic cases they put in the overheads after they watched that Clooney movie, and the self-entitled moaning they excel at when told they aren't going to get "free" alcohol just because the plane left 10 minutes later than scheduled. Americans on EU/Asian airlines are almost always lively in comparison... Though generally avoid star alliance because the Americans who couldn't get on the United flight will be on there.

Never use in-seat entertainment. Take some headphones with you, put on a podcast, and try to fall asleep. The headrest usually divides in three and will form neck restraints to prevent you from falling into your neighbour. Set the IFES to the sky map so that when you open your eyes 20 times during the flight you know exactly how far you've got to go.

Always, always drink juice or beer only. Water, wine, soda... They all make you go to the toilet.

Never take a seat near a toilet.

If it's less than US$50/hour to upgrade one seat class -- do it!

Get status. Don't care about free flights etc, they are very rare.... What is important is lounge access. Ever been delayed 3/4/5 hours? I have. Except, I was in the lounge eating and drinking relatively good, free stuff, and managed to watch a movie on my phone using the WiFi.

And finally, always, ALWAYS use "meet at the airport" to collect your car on return. Not having to take a shuttle etc seems no big deal, but honestly it feels like it's the worth every penny at the time!