The cultural differences between Tibetans and Europeans are so great that you could write extensively about this subject. Below are a few hand picked etiquettes to follow to help you during your time there.
Temple Visit: When visiting Buddhist temples or monasteries we ask you to adhere to the following rules out of politeness and respect for the local people. Do not wear shorts or miniskirts when visiting a temple. Walk always on the left in a stupa, temple or by a mani stone (prayer walls) (Ie clockwise).
Toilets: Public toilets in Tibet know absolutely no privacy. If partitions reach knee height then you're doing well! Moreover, most public toilets can be downright unpleasant. A hygienic advantage is that in Tibet people mostly squat whilst using the toilet, so you never need to contact any materials. It is recommended to make the most of the toilets in the hotel and in any case always have toilet paper (available in Tibet) with you.
General: Always remember that you are a guest in a country where one simply has different manners. If anyone is abnormal in this environment, it is you!