The Eighth Commandment of Blogging

Thou Shalt Apply Journalistic Standards To Thy Journalistic Entries

If you write movie reviews, op-ed pieces, or news commentary, stick to the rules if you want to be taken seriously. Argue your point of view, back it up with facts, and link to the sources of these facts. Show both sides of a story. Don't curse without good reason, don't yell, and don't use dubious rhetorical tricks.
Failure to do this will result in you preaching to the choir. Those who agree with you will get bored; those who disagree with you won't expect you to listen to them.