Your subject line should draw the recipient into the rest of the message. It should provide enough information that the recipient can guess at the content in the body of the message. On the other hand, the subject shouldn't be too long, or it won't all display. In a pinch, start the first sentence of the message on the subject line, put in an ellipsis (�) part way through, then continue the sentence in the body of the message. 
 

Establish a context 

When body language, tone of voice, and situation are lost, communication can fall apart. To compensate, introduce your messages more completely. You might want to tell the recipient the mood you're in, the events that led to the message, or the way that you know them. 
 

Be careful about humor 

Many messages containing ironic or sarcastic humor are horribly misinterpreted at the other end. Don't cut the humor, just make sure that people know when you are making a joke (ha!) It's not as impossible :-) as you might (giggle, chortle, snort) might think. 
 

Be careful about expressing frustration, anger, or complaints 

Minor complaints can sound like major anger without a context, especially if the recipient is in a defensive mood. So if you are complaining, make sure your recipient knows how you would like them to respond. Include something in the message to lighten the mood. 
 

Make it personal 

Putting the recipient's name at the top of your message in a salutation is a tiny step that makes any message much more friendly. Recalling a personal detail or shared experience also helps. E-mail is a sterile form of communication if you don't occasionally add these touches. 
 

Use selective emphasis 

DON'T PUT A MESSAGE IN ALL CAPITAL LETTERS. ONLINE, THIS IS SHOUTING!!!!! 
On the other hand, an OCCASIONAL word in all caps, surrounded by *asterisks*, or given its own line can help the meaning come out more clearly. Be careful about the bold, underline, and fancy font options in some modern e-mail programs. The message won't necessarily look as fancy to the recipient if they don't have the same program. 
 

Use more punctuation and symbols 

You can obviously go too far in trying to get your *$#!@! point across, but a few extra exclamations, question marks, symbols, or abbreviations (defined the first time you use them) can help make e-mail much more vivid IMHO (in my humble opinion). 
 

Consider privacy 

Remember that system administrators can read any message sent via e-mail if they are so inclined. It's also just a click of the "Forward" button away from being passed along to the person you complained about. Be especially careful when you are involved with mailing lists. When you reply with a joke to that message from your friend, you might accidentally be sending your joke to hundreds of other people.