Many dumb takes here, but also some good ones. Here are mine roughly sorted by importance:
(Don’t be a dick - obviously)
Choose a direct flight whenever possible. I usually would pick a shitty, more expensive airline over having a connecting flight.
If you are planning a connecting flight, try to allocate at least 1-1.5 hours for the connection. Planes are delayed all the time and the shorter the connection time, the higher chance you’ll miss your flight. Your checked luggage can also miss your connection, pack some necessities in your carry-on. (anything more than 3 hrs is overkill though)
Noise cancelling headphones/earphones: this is where they work best, blocking out the fatiguing drone of the plane. Highly recommended. Headphones are more comfortable over longer periods than earbuds.
Window seats are better for sleeping asile is better if you tend to move around (but people passing by will disturb you by brushing up against you and you feel the floor flexing more as they walk)
Cheap airlines: you get what you pay for. You will be treated like cattle but they do get you from point A to B for less money. Be aware they will nickle and dime you every step of the way, bring water (bottle you can fill after security) and some snacks.
Luggage: carry-on is better than checked if you can avoid it but sometimes you can’t. For cheap airlines double check the size limits for carry on. The sizes are not standard and cheap airlines try to trick you into paying fees. Sometimes they’ll also take your carryon during boarding to check it in the hold when the plane is very full. You can try to avoid this by queueing and boarding sooner than others, or by bringing a smaller bag that fits under the seat.
If you do end up checking a bag you’ll have to show up a bit sooner and usually wait a bit longer after the plane has landed. Place anything fragile in your carry-on! The luggage handlers throw your bag around like they are trying to break something on purpose. If you can’t avaid checking fragile things, surround them with clothes and other soft materials. Also put a luggage tag on your bag, sometimes multiple people have the same bag.
Flights during the evening and afternoon tend to have a higher chance of being late/geting cancelled. The effect is slight and there isn’t much you can do about it though. Just keep it in mind if you have a critical time/place to be somewhere.
On a long flight wearing your seat belt (even loosely) while sleeping means the flight attendant doesn’t have to wake you if there is turbulance.