Andy Ihnatko, of the Chicago Sun-Times (and many other online locations), has a post about his incipient comments policy, Towards a formal comments policy.
Yes, I know, I should be so lucky.
That said, I don’t think I’m going to improve on his principles much, if at all. Although, of course, the “I” in principle 1 will be me.
I will add, though, that if your comment is an exhortation to buy some chemical substance to better readers’ athletic prowess or otherwise unrelated to the topic in question, the spam button will be deployed.