Common element in the society in which you live.
Look at a common element in the society in which you live. Marriage is a good example. Try to explain this as if you were new to the whole concept. Ask yourself, why do people do it? How does it contribute to society? Is there any other way to accomplish what it does?
Now imagine that you are reporting to members of a different planet about your findings. Determine a sociological perspective to develop your analysis.