Don't leave your chopsticks in the bowl, it symbolizes death and is very bad luck.
Don't order one dish that you intend to eat by yourself. Thai meals are always shared.
Don't feel bad about adding condiments to flavour your food to your taste.
Don't wait for all of the food to come out before you eat it, Thai meals are leisurely affairs and the food just keeps on coming.
Don't use your fork to put food in your mouth, instead use it to push your food onto your spoon.
Don't look around for your knife - you won't need one as everything is cut up for you