Shut off your CAPS LOCK, use lower case, capitalize proper nouns, and punctuate as you would in a handwritten letter. Don't hog message space talking only about yourself. Leave some space for those of us who want to talk only about ourselves. Break your thoughts into short paragraphs to make your points. Don't be afraid to show your emoticons.
Brevity is the soul of acronyms.
Spare yourself keystrokes and conserve message space by abbreviating common phrases and expressions. For help with on-line slang, read A Glossary of Cyberspeech .