1. Avoid unnecessary profanity.
2. Avoid ridicule and sarcasm, especially when directed at other HNers.
3. Avoid complaining about "trolls" downvoting you. In fact, avoid discussing karma in general.
4. Avoid using emotionally laden terms of disapproval. Instead use direct objective language ("There were rendering artifacts in the rotation effects") or clearly state the subjective aspects of what you are discussing ("Something about the rotation effects rubs me the wrong way.")
5. Be concise and relatively formal in your language.