1) Show your respect towards the Royal Family. The Royal Family is very well respected in this country, therefore as much as possible, don't comment anything may it be good or bad about them. Don't ask controversial issues about them from the local people. It'll greatly offend them and neither talk to you about it.
2) Treat the Thai Baht money ( bill and coins) with 'respect' too. This means, you can't step on the Thai coins with your foot, in case it falls down.The reason? The King's portrait is on the coins as well as the bill, that's why it must be treated with respect. For Filipinos like me, we're used to hand the money, using our right or left hand..but here you'd notice they only give the money using their right hand as they believe that the left hand is for using somewhere else. Their bills here are very clean and no creases, while back home it's not that clean with "wanted penpal/ phone pal' messages all over it and folded 100 times over. :)
3) It's polite to 'wai' back when people 'wai' at you. Wyeing is a sign of respect. It's the folding of arms together like in a prayer gesture and bowing the head slightly.
4) Don't touch anyone's head, specially people older than you. The head is believed to be the most sacred part of the body so, it offends them when you touch their head.
5) Don't point your foot on people. Like when your sitting with your legs crossed, your foot must not point to a person. Just as they consider the head to be the most sacred part of the body, the feet are considered to be the lowest.
6) Don't go out with your hair wet, this is also considered impolite ( I've just learned this recently from a friend).