Strive for quality
Everything you post will contribute to the knowledge, the usefulness and the look of Debian. It will be publicly archived and found by others over time and in different contexts. Make informed comments, keep the information level high and the stress level low.
Work with others
Try to improve the quality of the community. Help to improve everyone's packages. Share your ideas and plans. Allow people to help and contribute. Thank people.
If you disagree with someone, explain your reasons. Listen to the reasons of others. You can live with disagreements as long as people can still work together. Convince people with results, rather than words.
Principles do not change, the rest changes with work
There are some things that you cannot change: social contract, DFSG. Everything else, you can completely change through your work.
Support the reasonable, rather than attacking the arrogant
When someone is behaving badly, supporting the victim of the bad behaviour helps to solve the situation much more than attacking the misbehaving person.
It helps both to undo the results of the bad behaviour and to show a better way of doing things.
Attacking the misbehaving person would just add tension, yet leave the victims with their problems unsolved.
For example, if someone got a bad reply with a rude RTFM or a rant, you can post a message with the real solution, some useful suggestions, or a more precise pointer to specific documentation. This will be helpful to the original poster, it will be useful information for the list archive and will serve as an example of a better way to reply.