common people

He is a common people.→He is one of the common people.

“common people”是复数名词短语，不能直接与不定冠词“a”连用。指单个人时，应使用“one of the common people”。

I come from a common people family.→I come from a family of common people.

“common people”是名词短语，不能作定语修饰名词。应使用介词短语“of common people”作后置定语。