I have always loved the final paragraphs of Edward Weston's essay Seeing Photographically...
"Now to consult rules of composition before making a picture is a little like consulting the law of gravitation before going for a walk. Such rules and laws are deduced from the accomplished fact; they are the products of reflection and after-examination, and are in no way a part of the creative impetus. When subject matter is forced to fit into preconceived patterns, there can be no freshness of vision. Following rules of composition can only lead to a tedious repetition of pictorial cliches.
Good composition is only the strongest way of seeing the subject. It cannot be taught because, like all creative effort, it is a matter of personal growth. In common with other artists the photographer wants his(her*) finished print to convey to others his(her) own response to his(her) subject. In the fulfillment of this aim, his(her) greatest asset is the directness of the process he(she) employs. But this advantage can only be retained if he(she) simplifies his(her) equipment and technique to the minimum necessary, and keeps his(her) approach free from all formula, art-dogma, rules, and taboos. Only then can he(she) be free to put his(her) photographic sight to use in discovering and revealing the nature of the world he(she) lives in."
(*) Amazing how gender biased this essay was at the time of its writing