Choose your destination. Containing 11 countries, and covering thousands of miles, Southeast Asia offers many possibilities. The biggest constraint is time. If you have one week, trying to visit more than one country will likely be too much. Travel in the region is always slower and more tiring than in Europe or North America. Keep this in mind as you decide which countries to visit, and where in those countries to go. If you have two months or less, it helps to focus either on the north of the region (Northern Thailand, Laos, Cambodia, and Vietnam ) or the south (Southern Thailand, Malaysia, and Indonesia). With more than two months, it becomes possible to see the whole region.
Buy your flight ticket. The earlier this is done, and the more flexible your dates are, the cheaper the ticket is likely to be. For a multi-country trip, it is often worth looking into "open-jaw" tickets, which allow you to fly into one city in the region and out of another. Peak times are during the Christmas holidays and the July-August season, so flights during those times are likely to be more expensive. Bangkok is the major air hub for the region, and the best place to start a trip.
Get your visas if you need them. The U.S. State Department maintains a website with individual profiles for each country. There is a section in each country's profile entitled "Entry/Exit Requirements" that will list whether you need a visa, or just a valid passport to enter a given Southeast Asian Country. Many travelers choose to fly to Bangkok, Thailand first, where they can enter for 30 days visa-free, and get their visas there. This is often cheaper and faster than doing so at home.
Get your immunizations. The website of the Centers for Disease Control and Prevention is a good place to look for what shots might be necessary. Do this at least two months in advance of your trip, as some shots require multiple visits to a clinic. If you have health insurance, check which shots it covers, as they are often several hundred dollars. The clinic you visit for the shots should also be able to prescribe you with medication to prevent malaria and treat stomach problems.
Buy travel insurance. This is very important. Most basic insurance policies won't cover the expenses of medical treatment overseas or being flown home in an emergency. More comprehensive policies will also cover cancellation of the trip, baggage loss, and provide life insurance in case of the worst.
Prepare your cash. An ATM card is the most basic item to have, but it is a good idea to bring both credit cards and an emergency stash of travelers' checks.
Pack your bag. Always bring less than you think you need. A lighter bag is always better, and you can cheaply buy anything you forget once you arrive.
Find a place to stay. Use a guidebook to find a few places to stay in your price range, and look at all of them before committing. Standards vary widely for a given price range. Don't let touts or "guides" bring you to a hotel, as they will claim a commission and you will pay a higher rate.
Eat carefully. Food is a highlight of any Southeast Asian trip, but it's easy to get sick. A few rushed trips to the bathroom is to be expected, but to avoid worse, be sure to be careful about what you eat. If the restaurant is empty or only serving tourists, it is a good idea to move on. Street food is delicious and would be a tragedy to skip - just try and avoid anything that's not cooked through. Bring water purification tablets and don't drink from the tap, and you should be fine.
Get around. Travel around the region is easy, with trains, buses, and minibuses the main way to get around. Short domestic or international flights are expensive, but a good way to avoid days on a bus. All the trips take longer than they would in North America, and you can expect the vehicles to be in worse shape. Always plan to arrive at least a day early anywhere you need to be, just in case. This is especially important for the flight home.
Meet people. Other travelers are good company and can give you the most current information on things to see and do. Don't just stay in the traveler areas, though. The farther from tourist areas you get, the more friendly the locals are, and as with any destination, the people make the trip. Learn a few words of the local language, and you will be a star.
