- Top-level comments should introduce arguments; responses should be responses to those arguments.
- Upvote and downvote based on whether or not you find an argument convincing in the context in which it was raised. This means if it's a good argument against the argument it is responding to, not whether or not there's a good/obvious counterargument to it; if you have a good counterargument, raise it. If it's a convincing argument, and the counterargument is also convincing, upvote both. If both arguments are unconvincing, downvote both.
- A single argument per comment would be ideal; as MixedNuts points out here, it's otherwise hard to distinguish between one good and one bad argument, which makes the upvoting/downvoting difficult to evaluate.
- In general try to avoid color politics; try to discuss political issues, rather than political parties, wherever possible.
As Multiheaded added, "Personal is Political" stuff like gender relations, etc also may belong here.