What is considered good behavior online?

Distance conveys a degree of anonymity and as a result many people feel less inhibited in online situations than in their everyday lives. This lessening of inhibitions sometimes leads people to drop their normal standards of decorum when communicating online. In response, good cybercitizens over the years have developed an informal set of guidelines for online behavior called Netiquette.
Netiquette can be summarized by three simple precepts:

Remember that there is a human being on the other end of your communication
Treat that human being with respect
Do not transmit any message that you wouldn’t be willing to communicate face to face.

Some specifics are:

Do not dominate any discussion. Give other students the opportunity to join in the discussion.
Do not use offensive language. Present ideas appropriately.
Be cautious in using Internet language. For example, do not capitalize all letters since this suggests shouting.
Popular emoticons such as ;0) or :0) can be helpful to convey your tone but do not overdo or overuse them.
Avoid using vernacular and/or slang language. This could possibly lead to misinterpretation.
Never make fun of someone’s ability to read or write.
Share tips with other students.
Keep an “open-mind” and be willing to express even your minority opinion. Minority opinions have to be respected.
Think and edit before you push the “Send” button.
Do not hesitate to ask for feedback.
Using humor is acceptable but be careful that it is not misinterpreted. For example, are you being humorous or sarcastic?