A good piece of writing can be written by most people.
Academic writing on the other hand, is usually written by the academic
(practicing or student) for the academia and the general public.
A good piece should contain:
A well defined topic.
A clear, informative, engaging and concise body.
Very good verbal skills.
Facts and other opinions with references.
An awareness of audience in the style of writing, with a bit of
artistic and oratorical constructs.
A concise conclusion, without much ambiguity obtained from the body of
the piece.