The Person on the Window Seat Gets Control of the Window
This is just the way it is, whether you like it or not. The person seated next to the window is the one who gets to decide if the window remains open or closed during the flight, because he/she is the person that feels the effect of sitting beside the window more than those on the other seats. If the person seated beside the window is willing to accommodate the 'window requests' or 'window needs' of those on the other seats, then that's nice, if not, they're just going to have to deal with it or they can politely ask an air hostess for a change of seat.
Give Everyone Their Personal Space
It's not uncommon for flyers to watch movies, series or TV shows on their mobile devices, or maybe even read a book, novel or magazine. However, no matter how tempting it might be, avoid looking over their shoulder or encroaching their personal space to watch with them or read with them. If you want to watch with them or read with them, you should first ask politely.
Invest in a Headphone or Earphone
When using your electronic devices, especially when watching videos or listening to music, be sure to use your headphone or earphones, to avoid disturbing those who are seated next to you, especially those who are trying to sleep. Additionally, aside from using a headphone or earphone, be sure to go a step further and ensure the volume isn't so loud it defeats the purpose of using a headphone or earphone altogether. Try to listen at appropriate volume levels when using your headphone or earphone, it might not be very convenient for you but the flight won't last forever, and when it's over you can do whatever you want and increase the volume to whatever level you want.
Be Aware of Your Surroundings
Before engaging your neighbor in a conversation mid-flight, be sure to check for signs of interest. If your neighbor is reading a book or using headphones, try to refrain from engaging in a conversation. If you must, then you can briefly interrupt the person, and watch to see how the person responds. If the person is quick to plug their earphones back in or is quick to return to reading his/her book, the person is probably not interested in a conversation.
The Middle Seat Gets The Arm Rest
There is no question about this, the person sitting in the middle seat has sole ownership of the arm rest. This is because, the middle seat can already be quite uncomfortable and restricting, so it's quite unfair to make it worse for the person by the depriving him/her of the comfort of resting his/her hands on the arm rest.