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?

In times of crisis it is of the utmost importance not to lose your head (Marie Antoinette)