Cover only a single topic per message and keep it short. This facilitates indexing, forwarding, and replying, and makes the best use of your readers' time. Don't use italics, underlines, or other special characters. Use commonly available letters and punctuation that any e-mail system can handle. This is often used at the beginning of each line to quote the relevant portions of the original message to which you are replying.
Messages written only in upper case letters appear to be shouting at the recipient.
Surnames, however, should be capitalized to tand out. Cite your sources. Listen before you speak. Take some time to hang out in a chat group, newsgroup, or mailing list to get accustomed to the group's standards and expectations. Your words are your verbal self-portrait which may be seen by an audience of hundreds, so select words carefully.