Why: You don't want to insult people. And like it or not, you are a goodwill ambassador for your country.

7. Give wisely. Never give gifts to children. Rather, find out what's really needed in a community (from schoolbooks to balloons), and give to local programs like schools (ask your concierge or tour operator for school names). Giving to local charities that can help a large number of people is the best idea of all.

Why: It may sound cruel not to give directly, but if you don't give kids money, they may stay in school rather than choosing a life of begging.

8. Pay the "gringo tax." While there's nothing wrong with bargaining—it's part of many cultures—avoid overly aggressive haggling for souvenirs, particularly in developing countries. Have some respect for the seller: pay a fair price.

Why: You probably earn at least 10 times as much as the merchant. Why shouldn't he or she earn a little profit?

9. Ask Before You Shoot. Ask locals for permission before you photograph them.

Why: You want a stranger to get your permission before snapping a photo, right?

10. Stop Drinking! Bottled water, that is. Reduce water bottle usage when you can. But be smart: don't drink the tap water in developing countries.

Why: Buying bottles is wasteful. You wouldn't leave your bottles on your best friend's lawn after a barbecue, why would you leave them at the base of a World Heritage site?

11. Save water. It may feel delicious, but don't let the shower run for half an hour.

Why: Water is precious in many countries, and tourists tend to use far more than local people. In the Mediterranean, for example, travelers use almost four times more water than locals, according to a 2004 WWF report "Freshwater and Tourism in the Mediterranean." Not long ago the Mayor of Capri blamed tourists for the fact that his city had "run out of water."

12. Conserve energy. Turn off lights, the television, and air conditioning when you're not in your hotel room. Opt out of daily washing of sheets and towels.

Why: Not washing towels may save the hotel money, but it will also save water and electricity, plus cut down on use of environmentally damaging detergent.

13. Bus It. Use public transport rather than renting a car. If you do have to drive a rental car, make sure it is well tuned and that the tires are fully inflated in order to increase your mileage and cut gas costs.

Why: Traveling on buses and trains saves gas and gives you the chance to interact with local people—plus it's better for the environment.

14. Buyer Beware. Be careful what souvenirs you buy in terms of materials used to produce them. Are they made from coral? From endangered animals? From native forests? Also, avoid souvenirs that aren't made locally.

Why: Cheap souvenirs made in China do nothing for the local economy in Mexico. And not only is it environmentally harmful to buy items made from endangered materials, it's sometimes illegal (such as in the case of ivory).

15. Pack Your Batteries. Take your batteries home; don't put them in the trash in developing countries.

Why: When batteries corrode, they leach toxic materials into the ground, contaminating groundwater often used for drinking and recreation.