... but, in general (and in addition to those mentioned above):

• Speak softly and quietly. Never raise your voice, never throw a temper tantrum . . . it will do no good, & will get you nowhere.
  
• Don't emabarass a Thai in front of other Thais. He/she will lose face (and so will you), and it will be looooong remembered!
  
• Don't criticize ~ in any way, or even in jest ~ the King or the royal family in front of other Thais.
  
• Don't wai. As mentioned above, the best answer to a wai is to smile and nod your head slowly.
  Wai's have specific height levels (i.e. as low to chest level or higher to the head and every point in between) which are meaningful to Thais but generally unknown to farang. If you feel you must return wai, then pay attention and try to wai up to the same level as you have been wai-ed to.
  A wai is a gentle and soft movement of the hands upward. Don't move them up fast or make the act a hurried one.
  
  In general, don't initiate the wai unless it is to your girlfriend's or boyfriend's parents. A low greeting wai initiated by you is appropriate to them, or anyone in the family olderthan them. Also a 'goodbye' wai. The family members who you are greeting who are younger than the parents, or you, always initiates the wai, and you can respond.
  Never wai Thai children ... it's bad luck!
  
• Don't point at Thais. They consider it very rude.
  
• Try your best to learn ~ and use ~ some rudimentary Thai phrases.

You can easily get along politely in Thailand with these few "rules". Inadvertant faux pas's on your part (far too much 'wai-ing' being the usual one) will normally be taken lightly and with a smile, so don't sweat the small stuff (probably with the exception of Royalty criticism).

Cheers ...