Same advice as knoxvillecouple!
Good attitude usually always means good trips, no matter what happens.
Pack light!
Be polite, humble, and respectful. You are entering someone else's world, not the other way round.

Follow the locals to the best cafe/restaurant and try the local dishes!

Pack as little as possible and buy at least half of what you need during the trip -- bring the new items home, even things like shampoo: they will extend your impression of being on vacation for as long as they last.

Stop and talk to the locals (in their language, if possible) and enjoy their parks. It's the best way to 'feel at home.'

pack light and bring home lots of mementos

Remember that this is your VACATION! Enjoy it with a light heart and you will never regret it. Let yourself get angry by petty mishaps, and you'll never forgive yourself.

The more you try to see the less you see.

Smile alot and always remember it is their country.

Bring a small packet of photos of the area that you live and also photos of family. It's a great 'ice-breaker' and folks love to see where you are from.

I live in the redwoods and purchase several postcards from my area to share or give away. People love to see the giant trees.

To second GreenDragon, remember this is your vacation! However much there is to see and do, relax and enjoy so that you don't return to work more stressed than when you left.

ditto everything said and..

remember, you are an ambassador of your country, represent it well

Take lots of photos. No matter how wonderful and amazing your trip is. No matter how slow or fast you take it. When you see something that makes you smile, or wonder, or ponder, snap a photo. When you get home, you can relive all those moments again and again.

We like to buy a cd or 2 of the local music & listen to it while in that particular area/region/country.

When we listen to it at home it reminds of our lovely memories.

Try the local food!

Bring a change of clothes in your carryon should your checked bag go astray(as mine has twice)

Make your flight there; make your flight home; whatever happens in between -- whether it was planned or not -- is all part of the adventure. RELAX!

And I second the one about calling the credit card companies. One year we traveled in the Pacific Northwest...for 5 days we had been making charges in the Olympic National Park...but then we cross over into Victoria, British Columbia, and may credit card company puts a hold in it.

Good advice everyone.

If things go awry take a moment to breathe, collect your thoughts and know that if handled properly it'll make a great story. Don't let small things put a damper on your vacation.

When lost in a big city without a map, find a big hotel and ask directions. They're usually very helpful and
will have maps handy.

Pack a lightweight duffle in your suitcase and fill it with dirty laundry to check on the plane when you go home. That frees up space in your carry-on for your purchases. Don't pack any valuables or new purchases in your checked luggage, if possible. I had my Paris flea market finds stolen from checked luggage.

Wear/bring comfortable shoes! Being in Europe means walking, walking, walking and lots of cobblestones.
((c))

Keep your sense of humor and heed all the advice given up to this point on this thread!!

Bring an illuminated magnifier. So that you can read the very small print on maps such as the Paris Metro map.

To reiterate what cmcfong said...Smile.

There is a great deal of wisdom in those 5 letters.

Don't think it was mentioned but make photo copies of your passport & CC's you bring (including their help phone numbers) & keep the copies separate. Really helps if lost.