Make sure to wear your comfiest sweatpants. I'm always surprised to notice how so many other passengers wear the most uncomfortable dress shoes, and restrictive clothing and it is always a dead giveaway for a rookie plane passenger.
Bring your favorite thing to read or play. There's going to be a lot of downtime and it goes by much faster when reading a book.
Get ready to have your personal space redefined to six inches on either side of your body for the next ten hours. Its not too bad, until you try to sleep and finally realize that your chair only reclines nine inches but the person behind you is limiting that to five because "hes trying to eat", and he'll be using that excuse for the rest of the flight. If your felling a little gutsy however, you can always pretend to stumble on them when you make your trip to the bathroom when you experience a "sudden turbulence".
Another great item to bring is chewing gum and a blindfold. Chewing gum helps get rid of the ear popping from reaching high altitudes. The blindfold reduces light from that neighbor who leaves his window blind open the whole time.
