I am not what you would call a global traveler. Most of my flights and travels are within the US. So when I do take trips out of the country, i always realize that it's the little things that trip you up.
Here is my small collection of tips, and hope they help you
1. Upgrade. Do it. Even if just to extended leg room. Do it. Don't think.
2. Business class. An expensive but well worth it option for any flight over 6 hours. Unfortunately, you don't usually get those upgrades with status only.
3. Bring a pen. You need it for the entry forms and the flight attendants don't have them.
4. Comfort is everything. Flying back from the UK, I sat next to a woman in a very tight short skirt, a load of spangly jewelry and made up to the nines. Besides waking up with raccoon eyes, her skirt was a wrinkled mess and she lost one of her spangles.
5. Stay warm. Layers are good. Bring your own blanket; you can buy ones that fold up pretty small.
6. Pillows for night flights are good ideas. The pillows provided don't help much. You can get ones that are inflatable and ones that will fold up on a little bag.
7. Tissues. I always try to fly with cold meds and tissues. Got caught recently without and paid the price.
8. Global entry. GE includes TSA Precheck, so go ahead and pay the fee if you think you will travel frequently.
9. BYO Snacks. Usually pack some healthy snacks in my bag. The food on the plane, especially in coach, will not be great.
10. Bring stuff to do. Most planes are starting to use more wifi enabled entertainment options. You will need a smartphone or tablet to access the movies and other entertainment.
11. Bring extra power - sticks, mophie, reserve batteries. Not all planes have power plugs and not all of them work when they do have them.
12. Don't forget to get up. The worst thing you can do is not move. If the flight is turbulent, do some simple foot stretches. Go up on the balls of your feet and push down for 30 seconds. Then your heels. This stretches your calves. The point is to avoid circulatory issues that can lead to serious complications and you don't want that, especially in a foreign country.
Let me know if you have other great tips to share as well!