It's easy to forget that there is a person behind the other computer. While on the Internet we can behave with the same ethics and standards of behavior that we do offline. We don't see facial expressions or gestures or hear the tone of voice, so we need to focus on communicating well.
Apply the Golden Rule: Treat others as you would want them treat you.
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 or bashing is defined as an online exchange that becomes nasty, insulting, or derisive. Use Netiquette rules to avoid damage caused in exchanges that become flame wars. Know your community, think about your posts, don't respond too quickly, clear up mistakes.
Avoid things that could be considered improper conduct, such as an angry tone or all caps.

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.