It's easy to forget that there is a person behind the other computer, but try to remember. We can't see facial expressions or body language, so words can easily be misinterpreted. Be the same person online you are offline — which has two meanings: first behave with the same ethics and standards of behavior online that you do offline, and second feel free to let your personality show in your work and communication.

Bottom line: be respectful, professional, and careful about what you say and how you say it.

Spelling and grammar will impact your image.  Txt abbrevs R OK 4 ur BFF, but AFAIK, your Instructor will not appreciate them.  This is no AFJ (April Fools Joke).

KISS - Keep It Simple, Students.  Use clear writing and good form.  And remember to use your Spell and Grammar Checker.

Flaming is what people do when they express a strongly held opinion without holding back their emotions. It's the kind of message that usually gets a strong reaction from readers. Although flames might appear to be fun to write and to read, Netiquette forbids the perpetuation of flame wars -- a series of angry messages, most of them from two or three people directed toward each other that can dominate the tone and destroy the camaraderie of a discussion group. It's unfair to the other members of the group.

Use a meaningful and concise subject line so your Instructor and classmates will have a clear idea of your topic and ideas.

When someone makes a mistake -- whether it's a spelling error, a so-called stupid question (there may not really be stupid questions), or an unnecessarily long answer -- be kind about it. If you decide to inform someone of a mistake, point it out politely, and preferably by private email rather than in public.

Internet or email messages written in all caps are generally seen as SHOUTING, and that's considered just plain rude. 

Judicious capitalization to highlight an important point or to distinguish a _Title_ or *Heading* is acceptable.  Or use the underline and * symbol to set them apart.