Recognize and respect the fact that your connections on Linkedin are real people. This should be guiding light in defining what to post and how to engage.
There's no simple rule of how to post just like there's no simple rule as to what to say in person.
Engage online just as you would in person.
Litmus test: Are you embarrassed when you meet your Linkedin friends in real life? Is there a disconnect between your online self and who you really are?