This is as much a practical question as a philosophical one, and from that perspective, I would say this: Remember that nearly everything you post on the internet is archived and searchable, including email, so try not to put anything out there that you wouldn’t want people to be able to connect to you ten years from now. I think we all forget that rule from time to time, but we do so at our own risk.
Other than that I think people should try to conduct themselves on the internet with some version of the same standards they would apply in person. The internet is an opportunity to create a new persona, but you should try to make it a better persona, not a worse one. Be kind and helpful to those you encounter, even the “newbies,” treat others with graciousness and politeness, strive to accomplish good things and avoid negative ones. No one meets those standards all the time, of course, but that’s an ideal to strive for. When you look back at your old posts a year from now, you’ll be happier to see a compilation of witty and appropriate comments than a record of flame wars, random trolling, and pictures of your butt.