Clear – makes the reason for the document plain at the first reading.
Correct – use correct grammar, spelling and vocabulary. Because your document happens to be business or technical writing, there is no excuse to eschew correct punctuation and spelling.
Concise – straight to the point. No need to use flowery or overblown language (see what I mean?).
Complete – ensure that you have included all the necessary information and be sure that you have answered all the questions before the reader asks them.
Concrete – be specific, do not digress.
Courteous – be polite. Remember that you catch more flies with honey…
Coherent – make sure that your message ‘hangs together’ in a logical, flowing manner and that it is easily understandable.
More information can be obtained from Google Answers.