Thai temples are very accepting of all visitors who want to come and visit, though there are a few important points you need to keep in mind before entering a wat. The first is dress code. As a general rule, you should make sure to keep both your shoulders and knees covered. It’s not always easy to dress this way in the stifling heat, of course. That’s why you might want to bring an extra pair of light pants in your bag to put on over your shorts before visiting a wat.
Sometimes a temple might have long pants or sarongs available for visitors to borrow, but this isn’t always the case. Men can often get by with shorts that come down to their knees (with the exception of the Grand Palace in Bangkok where long pants are required.) Generally speaking, the dress code is going to be more strictly enforced for women that it will be for men.
But sometimes you’ll visit a temple and see both local men and women wearing short shorts with no issues. What gives? The reality is that the rules are not always enforced, though you can’t really know in advance how strict things will be. Sometimes the monks or other staff may just be too polite to say anything.
Another important point is that when you enter a viharn or ubosot, you need to remove your shoes. This will be obvious by the loads of shoes left outside the entrance. When sitting down on the floor, be sure to sit cross legged and don’t point your feet toward the Buddha statue, as this is a sign of disrespect.
Taking selfies inside a temple is supposedly frowned upon, though local Thai visitors do it all the time, even in front of Buddha statues. In practice, this seems to be more of a gray area. General photography in most areas of a temple is fine, except when there’s a sign specifically telling you it’s forbidden.