*Do be very observant as to what other people are doing and how they are doing it as it will help you avoid embarrassing yourself.
*Don't stare at anyone.
*Don't touch anyone.
*Don't blow your nose in public, it is more acceptable to sniff.
*Do be careful about shoes when entering buildings.. usually you will need to remove them in the "genkan" at the entrance. Don't but your bare or socked feet on the genkan floor and don't put your shoes on the interior floor (past the genkan).
*Do make sure your socks are clean and not holed.
*Do make sure you and your clothes are clean!
*When using chopsticks don't drink with your free hand.. put the chopsticks down first.
*Do talk quietly and as little as possible.. it will reduce the chances of you being considered obnoxious!
*Do bring small presents with you from your home country. There is a good chance people will do things for you or give you presents so good to have something to give them. (But give it to them quietly and play it down - don't make a fuss about it.)
*Don't talk about yourself, your abilities or what you have done too much. If you are asked be MODEST!