A common mistake I use to make on LinkedIn was not keeping InMail and invitations personal. In other words the recipients thought I had sent them another message along the lines of Viagra spam.
The LinkedIn InMail tool does a good job of allowing you to create targeted, meaningful messages and save them as templates for tracking and future use. The following list will help you craft messages that get results.
I commonly get over 35% response rates on messages I send.
Subject Line: (Specify the industry) Career Connections
So, after many years of reading blogs and tips and hints etc, I have decided to start doing it myself.