Responsible Tourism -- Tourists in Vietnam are a relatively new species, and it's important to respect local culture and try to minimize our impact on the country. In Vietnam, try to keep personal ideologies and political debate quiet. Vietnamese are proud of their triumph over outside threats, autonomy that came at a great cost in lives and suffering, and the doors are just opening after a long period of isolation (because of both external sanctions and internal policies). The common sentiment among Vietnamese, more than half of whom were born after the end of conflict with the United States, is to forget the past and push on into an ever brighter future, economically and socially. There are, however, many monuments to Vietnam's years of struggle. When visiting monuments to war -- or one of the many sights that depict or revisit the years of struggle against the Chinese, French, or Americans -- it's important to practice restraint. Refrain from jokes, try to go in smaller groups, and engage in debates or personal feelings in discreet tones or at a later time. In places like Ho Chi Minh's Mausoleum in Hanoi, the monument to the My Lai Massacre in central Vietnam, the tunnels of Cu Chi and Vinh Moch, the Hanoi Hilton, or the War Remnants Museum, discretion is not only requested, it's often enforced (visitors have been known to receive actual hand slaps and barked orders at Ho Chi Minh's Mausoleum, for example).
Our strongest impact as visitors is through our money and how we spend it. Giving gifts in Vietnam, particularly to young people or the many who approach foreign visitors with calls of help, is a double-edged sword. Where it might gratify in the short term to help someone and fill a few outstretched hands with sweets or school supplies, it sets up a harmful precedent and props up the image of foreign visitors as walking ATMs -- to be bilked, begged, and bamboozled at every turn. You will be followed and harried in Vietnam quite a bit, and in some areas, particularly Hanoi, the young book-and-postcard salesmen and touts are part of organized gangs and very persistent (although the hard sell has lessened with the increased number of tourists). Saying a polite but firm "No" to persistent hawkers goes a long way to alleviating the problem.
Among Vietnam's ethnic minorities in the Central Highlands and the far north, be most careful about your impact. These are communities that are on the fringes of Vietnamese culture, distinct enclaves where ancient practices of animistic faiths still hold sway. Photographers should be sure to ask before snapping portraits or images of ceremonial sights; increasingly, asking for permission to photograph is met with pleas for money, but say "No" and move on. It's important not to assault locals with a camera, however uniquely attired and exotic they may be. Gifts of clothes or medicines might seem helpful but only diminish already-eroding ancient cultures and customs of clothing manufacture -- where, in fact, one's clothing is an integral part of status in the community -- and traditional medicines, erasing ancient traditions passed on from the time of migration from China. Learn about these people and their traditions as much as you can before traveling among them -- in fact, your knowledge about any place that you travel makes you less likely to make uncomfortable blunders. Keep an open mind, and be ready to learn, not teach. Below are a few good guidelines for environmental and cultural stewardship.
Don't litter: Sounds simple, but in a country where you will rarely find a public trash receptacle (most things are discarded on the street and swept up en masse), it is difficult. As unimportant as it might feel to drop a gum wrapper, more important is your example of not dropping a gum wrapper. On rural hiking trails or in national parks, tie a garbage bag to the outside of your pack and pick up wrappers along the way. Don't preach, but if locals ask what you are doing -- and they certainly will -- explain that you are keeping the park clean and that it is something that anyone can do.
Wherever possible, try to support the local economy -- eat at local joints, buy essentials like bottled water and soap at small mom-and-pop shops instead of big air-conditioned department stores, even try public transport (if you are a hearty soul). Don't buy any animal products, even the likes of snake wines or lizard-skin bags, and try to find out if souvenirs are produced locally.
Your behavior as a tourist also reflects on the many tourists who will come after you. Set a good precedent, even when if doesn't feel important.