DO give the middle seat the arm rest – If you’re in the window seat you get the window view and something to lean on if you want to sleep. If you’re in the aisle seat you can stretch your legs in the aisle and get up whenever you want to. If you’re stuck in the middle seat you don’t really get anything so the least you can have are the arm rests.
DO be polite when needing to use the bathroom – Please politely ask those next to you to move when you need to get up out of your seat.
DO stay in your own seat area – Most people only pay for one seat so that means you get one seat. Don’t man spread into your seatmate’s seat or invade their personal space.

DON’T bother them if them seem busy – If your seat mate is doing work, watching a movie, or listening to music please don’t start a full conversation with them.
DON’T eat smelly food – This is a courtesy or only to your seat mates but the entire plane.