To get wordy and all Dr. Phil on it I'd offer the following suggestions:

• Try to address issues not posters. 
• If you have an opinion on something state your case, don't ask others to state theirs when you know in your heart that it will be contrary to yours and will only lead to argument as neither of you will yield. 
• When trying to present an opposing viewpoint respond with ideas and data relevant to the issue, not insult and innuendo that smears the poster. 
• Trashing the news sources of stories is lazy; point out why what they offer is suspect or wrong.  Using Moonie Times, Faux News, ABSleaze News, etc.are hardly conducive to civil give and take. 
• No one owes you an explanation.  If your question goes unanswered assume they don't have a reply or an opinion and move on. Don't badger people.  Often an unanswered question is all the answer you need.
• Graphics are tough.  They are often divisive and created/offered with the intent to cause anger as much as amusement.  Think it through before posting such things.
• Altering politicians' names is not witty but rather counter productive to engaging in a dialogue. Doing so shows from the start that you are here to lecture and bully, not discuss.
• Recognize that you can't prove many opinions wrong, only disagree with them.
• Try to avoid using the plural "you" when addressing a singular "you".

And the obvious:

• Do not insult or name call other posters.  This includes saying things like, "Anyone with an ounce of sense can see..."  That is your opinion and it is an insulting and marginalizing way to state it.
• Never refer to posters family members except in a gracious and respectful manner - and not as a contrast to the posters themselves.  They aren't posting here and so mention of them by anyone other than the posters themselves should be kept to an absolute minimum.
• Try to keep it good natured.  Of course the kind of subjects addressed here will cause passionate responses, but take a minute before ripping somebody a new one. Don't discipline your children mad, don't drive mad, don't post in the Lounge mad.
• Be respectful.  Assume the person on the other side of the argument is actually good rather than starting with the idea that anyone who disagrees with you is stupid, hateful, etc.
• Do not question the administration of this site on the board.  If you have a problem with something send an email through the admin link.  A single email to that address goes to all admins including Mud and even the ones who don't come here often, so you can be assured no one person such as myself is hiding anything or going all Napoleoan on the board.

I readily admit I have been guilty of most of the things I caution against above, but I truly try not to and will redouble my efforts.  Hopefully if we all try our best we'll continue to enjoy this forum and benefit from the shared knowledge, resources, experiences, and varying viewpoints of those that post here.