When I visit...I make sure that I always know how to get back to my hotel/hostel. If I am in a country where I do not speak the language, I carry the hotels card or a matchbook with their name and address on it.
If you're in Mexico and a nice looking man asks to meet you at the "disco," don't go.
Always have an emergency $20 rolled up somewhere in your wallet.
Duct tape is essential for any trip.
Gnats go for the highest part of your body. So if the little flies are "bugging" you, raise up your hand above your head.
When I visit France I always make sure to brush up on any important phrases I may have forgotten. The French are more willing to help when you at least attempt their language. And besides, its part of experiencing the culture.
When traveling anywhere I always make sure to check for student or youth discounted flights so that I can get the best deals possible.
Take only what you need. Anything more, and you'll regret the back soreness from your oversized and unnecessary luggage. Oh, and beer makes a great laxative.
I always pack in layers and utilize dark colors. I also pack with ziplock bags to help use the space in my backpack better.
Wear Sandals through the airport and comfortable clothes on the ride. It makes everything easier