This is commonly referred to as "Netiquette" (internet-etiquette). Netiquette includes: how to convey emotions, what NOT to do on campus computers, and other common courtesies when accessing a network. Being honest and expressing yourself freely is very important, but being considerate of others online is just as important as in the classroom. Make every effort to be clear. Online communication lacks the nonverbal cues that fill in much of the meaning in face-to-face communication.
A useful practice pertaining to Netiquette is the use of "emoticons." These use combinations of different keyboard characters and letters to create pseudo-facial expressions or abbreviations that convey meaning.
Examples:
Emoticons
Abbreviations
Here are some links to learn more about Netiquette