They are all synonyms but you should be more careful with "common". "Common" refers to something normal or ordinary. In another context, however, "common" may refer to "an equally shared" within a specific group of people, community, nation, or culture. So in your case you may say: "I live in a common Chinese town." - to make it clear that the "common" includes typical Chinese standards and features or that the property of the town is shared by its citizens (see the definition of "common" here http://www.dictionary.com/browse/common). "Normal" and "ordinary" have more general meaning: "I live in a normal/ordinary town." - this means the town is very average, plain or undistinguished. Depending on who are you talking to, the listener may imagine the typical town features of his/her culture or place of origin. (See the definition of "ordinary" here: http://www.dictionary.com/browse/ordinary.) Conclusion: they are synonyms and may be used to point out very similar features, but it is always good to specify what category the features refer to.