I'm a former flight attendant. Here are 12 ways passengers ruin their experience on long-haul flights.

As a travel writer who used to work as an international flight attendant, I've crisscrossed the globe many times over.

I've serviced every cabin and sat in just about every seat on the plane, from a first-class sleeper suite to the middle seat in the last row of economy. In doing so, I've learned many of the tricks of the trade the hard way.

Here's what I've noticed many travelers do, consciously or subconsciously, to sabotage their comfort and overall experience on long-haul international flights.

Don't assume you can wash down a sleep aid with a couple of drinks and stay comfortably asleep for precisely the right amount of time.

Some sleeping pills can lead to grogginess and other side effects, and you need to be able to be awake and alert in the case of a mechanical issue or other emergencies on the plane.

If you have a hard time getting up after trying sleep aids for the first time, having a stronger-than-usual reaction to one, or taking too many sleeping pills, you could wake up to a frustrated flight attendant in front of your face.

Always talk to your doctor before taking prescription medication in the air. And if you're taking over-the-counter sleep aids, make sure you closely follow the instructions.

Some people swear by those classic U-shaped neck pillows, and my daughter actually loves hers.

But more often than not, I've seen passengers schlep them all over the world only to hang them up on the plane after finding them uncomfortable.

Before you burden yourself with such a bulky addition to your carry-on, test the pillow at home to make sure it's a good fit.

As a mom of two, I don't judge parents for loosening their usual rules to get their kids through a long flight. My oldest would happily hop on the world's longest flight just for the opportunity to watch TV and movies the whole time.

The amount of kids' TV shows, movies, and games on most international flights is glorious, but if you don't mix in some analog entertainment options — like coloring books, sticker books, or mazes — your kids will probably be too wired to wind down and sleep.

And without sleep, they'll probably experience jet lag the next day.

There's nothing like settling in for a long flight by kicking off your shoes and pulling on a comfy pair of socks, an amenity that crew members often hand out in first class.

But you're supposed to wear those socks when you're sitting down in your seat, not when you're walking around the cabin.

When I was working as a flight attendant, many airplane carpets didn't get deep cleaned very frequently. Because the cabin can get bumpy when the plane flies through turbulence, the liquid on the lavatory floor might not be water.

If you want to walk around without shoes on, pack some slippers to avoid direct contact with the floor.

It's hard to please everyone, and that's especially true when it comes to the temperature inside an airplane that's hurtling across the world thousands of feet above the ground.

There's a high probability that at some point, the cabin will be too hot or too cold for your liking. You can ask a flight attendant to tweak the temperature, but keep in mind that another passenger may have just requested a change in the opposite direction.

Play it safe by dressing in layers that are easy to pile up or remove.

A long-haul flight is a perfect opportunity to catch a new movie release or a TV series that streams on a channel you're not subscribed to at home.

But seat-back TVs can be finicky, so there's a chance the one in front of you won't work. If you're not the kind of person who can sleep all night on a plane, bring your own entertainment.

It's smart to load up your devices with movies, shows, and e-books before a long flight.

Just make sure to keep your devices fully charged before you board because it's not uncommon for the outlets in a seat, a row, or an entire plane to stop working.

To be extra safe, bring a book or download a few podcasts, which won't drain your battery and will help you stay entertained through the night.

Because of decreased blood oxygen levels from low cabin pressure and dehydration from low humidity, alcohol's effects can feel like they hit much harder in the air.

I've seen inebriated passengers embarrass themselves, start fights, and vomit after boasting about how much alcohol they can handle.

I'm not saying you can't have a glass of wine with dinner — I rarely pass up the opportunity — but please keep in mind that even if you don't misbehave, too much alcohol and dehydration can lead to a brutal case of jet lag.

If the captain is constantly switching the seatbelt sign on and off or you have to climb over other people to get to the lavatory, it can be tempting to ration your water intake on flights.

But the dry air and high altitude can both contribute to dehydration, which can then exacerbate jet lag symptoms or lead to other health issues.

Flight attendants should frequently sweep through the cabin offering water, but if that's not the case, don't hesitate to ask for more.

To have more control over the situation, you can bring your own water bottle on the plane. Most airports have water stations, so consider bringing an empty bottle to fill once you pass through security.

If you're in a premium cabin, a flight attendant may hand you a cute amenity kit. But if you're in the back, you'll probably have to bring your own.

The air in plane cabins tends to be low in moisture, so bring lip balm to keep your lips from chapping and lotion to keep your skin from flaking.

If you don't have noise-canceling headphones, bring earplugs to block out the sound of people chewing, chattering, coughing, and pacing up and down the aisles.

An eye mask helps cover your eyes from flashing TV screens, flight attendants' flashlights, and the light streaming in from any open window shades.

And after a long night of eating airplane food, sipping wine, and then waking up to breakfast and coffee, you'll appreciate having travel-sized toothpaste and a toothbrush. Or at the very least, bring a stick of gum to freshen up your breath.

Some airplane food is very processed, so it makes sense that travelers want to fill up on salads and fresh vegetables at the airport.

That said, do your best to lay off anything that can give you gas, including carbonated beverages. The low air pressure at cruise altitude causes gases to expand.

That's the reason your bag of chips inflates like a balloon, and it explains why you have to loosen your belt to accommodate your in-flight bloat.

All that trapped wind can be agonizing, which is why my airline trained its flight attendants to put passengers in flatulence-friendly positions to ease their pain.