Do'S and Don'ts in Business Invitations

Hi, I would like someone to help me with a project I have to do for university. I have to make a presentation on the do'S and don'ts in business invitations. What I mainly want to talk about is when you send letters to customers or to other companies about an event like the launh of a new product, so what you have to include in such invitations as well as what you shouldn't do or include. I know we should not use the informal approach, don't send out these invitations just a few days before the big event, are there any other don'ts i could talk about
i would really appreciate it