There are a lot of posts out there about how to survive a long flight and things that you should do, but these are the most important things NOT TO DO in order to enjoy (and not annoy fellow passengers) on your next plane trip.
1. Don't board drunk
If you can get on at all that is. The flight crew will not let anyone who is visibly intoxicated board the plane, so don't let one beer before you board turn into seven, or you might find yourself grounded.
2. Don't forget to bring something to do
A mistake I've made myself, remember that in-flight entertainment is not infallible. I made the mistake of boarding a 11-hour flight with only headphones thinking I could watch movies the whole time. The entertainment system failed and so I spent the entire flight listening to a screaming baby instead.
3. Don't bring smelly food
A flight is not the time to eat a tuna sandwich. If you are bringing your own food, make sure it isn't fragrant and avoid anything with nuts, as there are a lot of people out there with allergies.
4. Don't bring a carry-on that you can't lift yourself
If you can't lift your bag over your head to put it in the overhead bin yourself, it is too heavy. Take something out. (Note: Flight attendants actually aren't permitted to help you out as they can get injured lifting items that are too heavy).
5. Don't forget that everyone around you is trying to get comfortable too
Don't hog the armrests, and remember that there is a person in front of you and someone behind you as well. Don't slam your tray table open or kick the seat in front of you, and be conscious of what the person behind you is doing before you recline.
6. Don't drink booze, soda, coffee, or tea the whole flight
Unless you are looking to be dehydrated, bloated and sleepy, make sure you drink lots of water instead. if you must have something other than water, try to stick to just one glass of another liquid. Dehydration happens quickly during a flight and will make you sluggish and jet lagged when you land unless you try and counter it.