* CLEAR; Clarity of intention, idea, details and language.

* CONCISE; Keeping correspondence brief and to the
  point.

* CONSIDERED; Having thought about the writing, planned it and having
  considered the needs of the reader. 

* COMPLETE; Omissions lead to further correspondence.

* CORRECT; Format, language, tone and facts. At the very least mistakes create
  a poor impression.

* COURTEOUS; Being polite even when you are disagreeing with a correspondent.