I don't celebrate Christmas very much, because I am not a Christian, and it is also not a public holiday in China. But I work in a UK company, So I have one day off on Christmas Day.
I think Christmas is the most popular foreign holiday in China, almost everyone knows it, and there are quite a lot activities in Shanghai during Christmas holiday. The main streets and shopping malls will be decorated with Christmas elements.
Some people live in Shanghai will celebrate it just like a foreigner do, they buy Christmas trees and exchange gifts with their friends and family.
I celebrate it simply, I may eat a fancy dinner with family or friends, I think it is always good to find a sense of ritual in life.