This is a fantastic question. There are many ways in which to do this. So, let me offer three suggestions.
First, starting with some theories of cultural anthropological or sociology might be helpful. In a words, try to explain to your students that values differ from place to place. Plenty of examples will be the best way to get this point across. For example, taking your shoes off in Asians homes is important but may seem odd. To get this point across, you might say that this action is like walking with your shoes on someone's bed. Another example: in Japan old homes are looked down upon, but in New York, people love pre-war buildings. Things differ from place to place.
Second, another strategy might be to show how your students differ in terms of norms and practices among themselves. This can be a good segway to show differences in other cultures. Or you might start with how one generation differs from another. All of these underline the same point - different norms.
Third, a field trip might do wonders, if you are able to visit a place that shows different cultures. A good documentary might help in this area as well.