Everyone has their own code of ethics that they adhere to, whether they've ever itemized or even thought about them or not. Here are some of mine that I try to adhere to:
1. Try to make each post either informative, purposeful, or funny (including smart aleck, which can get dicey so watch out).
2. Though it can be difficult both to identify and to do, try to avoid responding to the sock puppets (those that obviously have a few different accounts here), and don't out them either unless they get real bad.
3. Don't "out" anyone by name. Responding to their post use their member-name, not their given name that you learned via PM or some other way. If they wanted their forum member-name to be their given name they'd have made it that way. Also it confuses other readers to respond to BBQ-Man's post by saying "Hi Tony"... and besides it only sounds like schoolyard oneupmanship anyway.
4. Don't "out" anyone in person. Like demanding a member go anywhere in person.
5. Don't "out" anyone's privacy or anonymity in any way.
6. Never use the word "WE" in your post, unless you also specifically itemize exactly who all you're speaking for. Otherwise it smacks of schoolyard bullying.
7. Never respond to another member with the idea that they're NEW here (and thus pointing out that you're not). Respond to the content of their post, or not, but playing the new guy card is a cheap shot.
8. Never post a picture of another member without their specific permission (except a picture they've already published themselves), except in a group picture where all the people in the picture are not specifically identified. Reference "outing"...
9. Never photoshop up changes to others' pictures and then post that.
10. Everyone sees specific members that follow other's around and post a negative comment (that isn't funny and has no informational value) every single time that person posts; that's really unattractive, though I won't use the "stalking" word; 99.99999% of Internet users don't understand what stalking really is and overuse that word.
11. Don't ever tell anyone that they SHOULD go buy something, not buy something, vote a certain way, or be in favor of a certain thing; instead post why YOU are doing a certain thing or thinking a certain way. i.e., don't be all pushy/intrusive.
12. Give rep. often and a lot, based solely on what is said in that one post; not at all based on what you might think of that member's other posts or of that member personally; this encourages good behavior from those that struggle most with having good behavior.
13. Give rep even more quickly in response to a member that has taken an effort, like posting their own food recipe, or even a process recipe, like how to make sepia pictures in photoshop, or change their profile/sigfile/avatar. Rep other's posted pictures easily and often.
14. Avoid labels like left, right, lib, and the like; there's no good to be done with doing so.
15. Avoid posting because you want to post, rather than because you have something about it to be said that hasn't been said.
16. Read more than you post. Compare your count of your List of Subscriptions with the number that shows your total post count; if the second number is 2+ times the first, you're posting way too much.
17. Post quality information. Compare your total post count to your rep count; if the first number is 4+ times the second then you're posting way too much.
18. Proofread your post by using the preview button; and do it again, and again, until you have read your previewed post and have no changes to make; then post it. Spell as well as you're able to, except when intentionally using expressions or for a specific reason.
19. Don't copy/paste entire articles from other sites, even if you do provide attribution; its cheap. OK to post an excerpt and a link to the whole/original version though.
20. Virtually never post anything as long as this list you're reading now, because not one person in a hundred will actually read down this far, so all that info you just wanted to share just became nothing more than a fart in the wind because you were too long winded.