In relation to audience, a thought crossed my mind, to which some consideration may be given in this context. It is the question "How much knowledge can I expect my audience to have?"
An example crossing my mind is Piers Anthony's series of "The Incarnations Of Immortality" - good and easy reading, if (!) you have a relatively clear understanding and knowledge of mythology (in this particular instance the graeco/roman -> christian thread). Or James P. Hogan's "Thrice Upon A Time" - lost me to some extent on the path of teoretical physics.
We have discussed before the need of researching, especially if the story is in a real or otherwise "given" (e.g. historical) context. But obviously one must find a balance between describing everything required to understand the context respectively the story, and not boring the reader with "common knowledge". But then again - what can you safely assume an average reader to know, and how do you determine that? Or don't you?