Here are things you shouldn't do:
Organize your luggage to save space is important. The lighter the luggage, the better. A large suitcase adds unnecessary stress and may limit carrying it onto the plane. Whether you're traveling by plane, car, or train, a small suitcase should be a priority.
Avoid exchanging money at the airport or train station due to obscene exchange rates and hidden fees. The safest place to change money is at a bank, even though the exchange rate might not be the best. You can ask locals or taxi drivers for more useful information.
Make sure to open the ventilation hole at least partially and wear a sweater if you're too cold. Numerous studies have shown that the cabin air contains bacteria and viruses, so it's advisable never to close the ventilation hole.
Wearing clothes that cover as much of your body as possible is recommended, as seats in public places like airports, planes, and cars are not always clean. Comfortable clothing will also help you sleep better on a plane and prevent deep vein thrombosis.
Starting 3-4 days before your flight, adjust your sleep schedule to match the time in your destination country. Go to bed earlier than usual if you're traveling east and slightly later if you're going west.
Having an official ID is essential in case you have a run-in with the cops. Always carry copies and keep the originals in a secure place.