Temple Etiquette

Thais are generally very forgiving by nature, and will rarely show it if you do anything to offend them. However, it's best to avoid giving offense in the first place by observing some very simple rules regarding the proper behavior for temples and other religious places. Here's a brief summary of how to behave:

Dress Properly
Bare shoulders and short pants should be avoided. This rule is somewhat flexible depending on the "rank" of the temple and whether you're a man or a women. Outside of the big cities you will often see men attending a temple in short pants and tank tops. While marginally acceptable for a man, it is totally unacceptable for a woman. Skirts or pants should be at least cover the knee. In high rank temples such as the Temple of the Emerald Buddha in Bangkok, as well as those royal palaces open to the public, you will not be allowed to enter unless you are properly dressed. In most such cases, there will be unisex sarongs available to make you more acceptable.
Watch Where You Point That Thing
Pointing, in general, is rather impolite. Pointing with your foot is downright rude. Following an old tradition from Hindu times, the head is sacred because it is closest to heaven, so likewise the feet are therefore the most unclean. When siting or kneeling in a temple building, make sure the soles of your fee are not facing the alter.
Take Off Your Shoes
If your feet are considered unclean, then your shoes are definitely dirty. You must remove your shoes before entering a temple building, or someone's house for that matter. Failing to do this one little thing is perhaps the most insulting thing you could do to a Thai person.
Do Not Temp the Monks
Being a monk means detaching oneself from all worldly occupations, even (or perhaps especially) sex. Therefore, it's considered rude for a woman to even attempt to touch or had something to a monk. If a woman must give something to a monk, the typical solution is to place the item on a table where the monk can pick it up. In merit-making situations such as morning offerings a monk will often have a layman helper to take things offered by female merit makers. This "service" is a form of merit making for the layman.
Stay Off the Buddha
Buddha images, no matter how small or old and decrepit, are sacred religious objects and must be treated with the utmost respect. Do not climb on them, sit next to them for a picture or put them on the floor -- or anyplace "inferior" to a person.