One of the great pleasures in life is a good meal and even greater pleasure is a Thai meal, perhaps the greatest, most relaxing, and totally satisfying culinary pleasure is a Thai meal with Thai friends in Thailand; the home of the world's truly great cuisines.
To fully enjoy the meal and to avoid any awkward or embarrassing faux pas, there are a few things that one needs to know and understand first. In general, you'll do fine if you adopt a humble "watch, learn, and imitate" attitude. For starters, what you don't want to do is, grab a plate or bowl of something you like on the table and scoop it all on to your plate.
If you're at someone's home, you won't have to worry about ordering, since everything will be prepared and brought to the table for you by your host. If you're out with a few friends or a group however - unless you know what you're doing - defer to the senior people at the table, who will most likely be running the show anyway.
The rule of ordering dishes for groups, is to order one dish per person plus one more; so three people might order four dishes and so on. Rice, although eaten with most meals, must also be ordered, and is frequently served person to person by the waiter. Likewise, once you order your drinks, you'll find them being magically refilled at most larger restaurants. Please keep an eye on how many bottles are accruing on your service cart to avoid over-charged.
Thais love balance as well as diversity in both flavors and textures. Thus when a number of dishes are ordered for a larger group, there will usually be a soup, often spicy; a curry, a fish or meat dish, a vegetable dish and a type of Thai salad (Yum). Depending on the restaurant, desserts are often an afterthought choice; frequently a large plate of mixed fruits will be ordered for the table which both refreshes and cleanses the palate.
Now for the important part: table manners. Table manners, being taught to us in childhood, almost seem like a natural, universal behavior - they are not; they are culturally determined. Accordingly, if you find yourself in another country, Thailand for example, you will be well-served to watch how they eat and follow suit. And you should do so in a calm, relaxed, gentle and deferential manner. This will go a long way towards earning you serious cultural capital.
From the outset, your meal will always arrive at the table in a seemingly helter-skelter fashion as they are completed in the kitchen and sent out. Because Thais do not generally care in which ordering particular dishes. It does not matter at what time of the day, they are just pleased to see any dishes coming and thus the meal commences.
At large meals, dishes are almost always shared and communal - except when they're not; someone may choose to order an individual dish for themselves, but this is more the exception than the rule. Typically, the dishes are placed on the table between all the diners. Then, each person takes modest spoonful and places them on his plate next to the rice.
These spoonfuls are then mixed with rice on one's spoon, which is in the diner's dominant hand - preferably the right hand - with the help of the fork, which assists with the other hand. The idea is to keep the dishes separate and discrete, to be enjoyed on his own, without mixing them with other dishes on your plate. When you think about it a bit, this all makes perfect sense, although it may take you some time to get used to.
You should also pay attention to what you take, especially avoiding piling up food on your plate that you cannot or do not eat. You are both taking this food away from others and essentially implying that you're not happy with this particular food that you've taken but not eaten. Make an effort to only take what you will eat and strive to keep your plate otherwise clean, save your diminishing stock of rice.
Reaching for anything with the left hand is to be especially avoided, since the left hand in many parts of the world, including Asia, is the hand of personal hygiene, the unclean hand. This will certainly be noticed by your fellow diners and very seriously frowned upon, whether they openly display their displeasure or not. In fact, this is possibly the greatest faux pas you could make at the table.
While on the subject of faux pas, or literally cultural missteps, the following is very important to bear in mind and to never do. Should you find yourself in a dining situation seated on mats on the floor, which is common in Thailand, sit with your feet under or behind you but most importantly; do not stand up and step over a person or the food. This is basically indicating to others that you don't care if you get other people or the meal dirty with what is on the bottom of your feet, the lowest part of your body. Actually, this is a strong competitor for the "left hand" faux pas.
The above prohibitions are not meant to imply that you must be self-conscious about following a large number of rules when dining in Thailand. They are meant to indicate that you cannot take anything for granted during such a personal cultural ritual as sharing a meal together. As everyone knows when visiting a foreign country, there are very specific cultural do's & don'ts for every distinct culture in the world.
By doing some research and learning before interjecting yourself into a new cultural environment, you'll not only avoid embarrassment and potential insult, but you will be admired and respected for taking the time to learn, practice local behaviors and customs. The best part of all is that, once learned, you can sit down with any group of Thais and truly enjoy a great meal of Thai food along with the legendary Thai hospitality and joy of life.