Wai appropriately. The wai is the gesture of putting your hands together in front of you in a prayer like fashion. This is a sign of respect toward people who are older or in superior positions. After the younger or subordinate wais, the superior returns the wai.
Because you are a foreigner, Thais won't expect you to wai first, but it will be appreciated if you do. Not returning a wai is considered rude, but Thais are very tolerant people and recognize that you may not know what or how to do something. How high or low your hands are when you wai and how far you bow when waiing are determined by the social status of the other person.
Shoes must be removed before entering people's home or temples.
Bend over a little when you walk in front of someone or between people.
Dress appropriately for the occasion. Wear good clothes to temples, government offices, and good restaurants.