If you want your flight to go as smooth as possible, you should adhere to an airplane etiquette. There are a few unspoken rules which will make your time on the plane much more enjoyable.
For example, you will be able to pass through security much faster if you first remove the things you have in your pockets. Try to limit your luggage to the things you strictly need, because the space is limited and oversized bags will only disturb other passengers. When on the plane, put your bags in front of you instead of carrying them on your shoulder. If you do that, there are chances you hit other people who already sat down.
If you feel your seat is uncomfortable, you can move to an empty one after the plane takes off. Don't occupy another seat until you are sure it will remain empty. When you are seated, try not to recline the chair all the way. Some airplanes offer more leg space, but this space is generally small and you will disturb the passengers behind you.
If you are traveling long distances, you may feel the need to take of your shoes. You can do that, as long as you wear cotton socks or use talc powder to remove sweat. The airplanes are confined spaces, and having a lingering smell around for hours does not make life easier on anyone.
Some people are more talkative than others. If you feel like chit chatting but your neighbor is not in the mood for that, don't bother them. If you have headphones, put them on and listen to your favorite music instead.
The more your travel, the more experience you will gain and these simple rules will become a habit.