Go pee before you get on your flight... the airplane restrooms are notoriously cramped and everyone watches you walk down the aisle to go.

Take some chewing gum for takeoff... it will help with the pressure change stopping up your ears.

Get a window seat... it's beautiful to watch things on the ground get smaller below you. Never take a middle seat if you can help it.

Get to the airport early in case you run into any unexpected delays.

Depending on how long the flight is they may show a movie. You can read. You can use a laptop although not during takeoff and landing. You can listen to music. You can use the time to do office/school work. The main thing to remember on long flights is that every couple of hours you should get up and move arround. Also if have a lot of pressure in your ears during take off or landing yawn, swallow, or chew gum.

I always load up my Mp3 Player with my favorite songs and bring plenty of books and magazines. Just remember to breath and you will have a Great flight.

Bring your favorite book or magazine.
Listen to earphones or an ipod with your favorite music.
Bring a small snack if you're not in first class.
Sleep if you want to because it passes time.
Play a game of Poker, Blackjack, or War. I played Texas Hold'em on the airplane and it was really fun. It passed about an hour of time up.
Make sure you go to the bathroom before landing starts. I remember I had to go to the bathroom so bad but the seatbelt sign was on. I was crying, I had to go so bad, oops. I drank a large pop at the airport and that really taught me a lesson.
Look out the window for a few minutes, it's amazing how you can look at the sky for 30 minutes. It was so bright outside and I really enjoyed looking at the clouds. Especially when you are landing, everything becomes in focus and it's just a beautiful sight.
Bring a laptop or a dvd player if you like. It really depends on how long your flight is. If you have a long flight, it might be a good idea to bring a laptop to keep entertained. Have a safe flight and Enjoy.

inside the plane is better than outside.

as to what your should do, depending on the length of the flight, sleep, read, knit, eat, drink.

forget about games, etc. so leave your horseshoes home. shuffle board is also not pratical

I give you the advice to bring a book and loads of loads of GUM. You can get real bored staring at clouds and counting your fingers. Trust me.

I agree with all of the above. I will add a little more: Eat a 'little something' before you "embark", but Do Not eat Tex-Mex, Italian, or anything spicy or gaseous. Nix the potatoes, beans, cabbage. No milk. No carbonated beverage. Some chicken or fish with some toast and raw veggie salad. That's all. And stay calm. It can be an enjoyable experience. Remember that you are riding on air currents that can support tremendous weights of metal, etc. far exceeding the craft you are in. And your craft is designed to "love" the air...and be loved in return. "Would you like to ride in my beautiful balloon?...Up, up, and away...in my beautiful ballon....OK, sorry,...(wink)

I get airsick so I take dramamine before flying. Loose fitting shoes help since feet tend to swell during long flights. Take your share of bathroom breaks. Helps with the boredom & gets you up & moving your legs. Take your own food as, although they may sell food, it may not be what you want. Take a book to read. Also, snag one of those pillows & blankets as you get on the plane. They're hard to find later on.
Have a great flight. :)

OK OK honestly? My best piece of advice is this:

Don't bring a bomb

Fight tooth and nail to get an aisle seat, and pray that you aren't next to smelly and/or obnoxious people.