* A paragraph explaining social networking and another paragraph explaining LinkedIn.
* A few paragraphs on the benefits of joining LinkedIn.
* A few paragraphs explaining that a LinkedIn invitation was special because it meant that the inviter trusted and respected the invitee and wanted to stay in touch professionally.
* A tiny blurb along the lines of "I’d like to add you to LinkedIn network."
Despite my expectations that one of the explanatory messages would be best, the short, vague blurb outperformed by a huge margin.