How to write a invitations like this?

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Hello, Mylotters, Can you give some clues about how to write a invitation in English? Well, I want to invite some guys to attend a ceremony of a store opening. by the way, to greet Christmas or something related, the main key is happy, joy or festive, so can mylotters help me about this? I'll apprieciate if you can give me some examples . So many thanks:) !